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Inverse Function Questions in English

Class 12 Mathematics · Relation and Function · Inverse Function

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Showing 43 of 144 questions in English

101
EasyMCQ
If $f(x) = \frac{a^x - a^{-x}}{a^x + a^{-x}}$,where $a$ and $x$ satisfy the necessary conditions,then $f^{-1}(x) =$
A
$\frac{1}{2} \log_a \left( \frac{1+x}{1-x} \right)$
B
$\frac{1}{2} \log_a \left( \frac{1+x}{x} \right)$
C
$\frac{1}{2} \log_a \left( \frac{2+x}{2-x} \right)$
D
$\frac{1}{2} \log_a \left( \frac{x}{1-x} \right)$

Solution

(A) Let $y = f(x) = \frac{a^x - a^{-x}}{a^x + a^{-x}}$.
Multiply the numerator and denominator by $a^x$:
$y = \frac{a^{2x} - 1}{a^{2x} + 1}$.
Now,solve for $x$ in terms of $y$:
$y(a^{2x} + 1) = a^{2x} - 1$
$y \cdot a^{2x} + y = a^{2x} - 1$
$1 + y = a^{2x} - y \cdot a^{2x}$
$1 + y = a^{2x}(1 - y)$
$a^{2x} = \frac{1+y}{1-y}$.
Taking the logarithm base $a$ on both sides:
$2x = \log_a \left( \frac{1+y}{1-y} \right)$
$x = \frac{1}{2} \log_a \left( \frac{1+y}{1-y} \right)$.
Replacing $y$ with $x$ to find the inverse function:
$f^{-1}(x) = \frac{1}{2} \log_a \left( \frac{1+x}{1-x} \right)$.
102
EasyMCQ
If $f: R \rightarrow R$ is given by $f(x)=7x+8$ and $f^{-1}(12)=\frac{k}{7}$,then the value of $k$ is
A
$7$
B
$1$
C
$4$
D
$8$

Solution

(C) Given $f(x) = 7x + 8 = y$.
To find the inverse function $f^{-1}(y)$,we solve for $x$ in terms of $y$:
$7x = y - 8$
$x = \frac{y - 8}{7}$
Thus,$f^{-1}(y) = \frac{y - 8}{7}$,which implies $f^{-1}(x) = \frac{x - 8}{7}$.
Given $f^{-1}(12) = \frac{k}{7}$,we substitute $x = 12$ into the inverse function:
$f^{-1}(12) = \frac{12 - 8}{7} = \frac{4}{7}$.
Comparing $\frac{4}{7}$ with $\frac{k}{7}$,we get $k = 4$.
103
EasyMCQ
If a function $f: R \rightarrow R$ is defined by $f(x) = \frac{4x}{5} + 3$,then $f^{-1}(x) =$
A
$\frac{5(x+3)}{4}$
B
$\frac{5(x-3)}{4}$
C
$\frac{4(x+3)}{5}$
D
$\frac{4(x-3)}{5}$

Solution

(B) To find the inverse function $f^{-1}(x)$,we set $f(x) = y$.
$y = \frac{4x}{5} + 3$
Subtract $3$ from both sides:
$y - 3 = \frac{4x}{5}$
Multiply both sides by $5$:
$5(y - 3) = 4x$
Divide by $4$:
$x = \frac{5(y - 3)}{4}$
Since $x = f^{-1}(y)$,we have $f^{-1}(y) = \frac{5(y - 3)}{4}$.
Replacing $y$ with $x$,we get:
$f^{-1}(x) = \frac{5(x - 3)}{4}$
Thus,the correct option is $B$.
104
EasyMCQ
If $f(x) = \frac{3x+2}{5x-3}$,where $x \in R - \{\frac{3}{5}\}$,then:
A
$f^{-1}(x) = f(x)$
B
$f^{-1}(x)$ does not exist.
C
$f[f(x)] = -x$
D
$f^{-1}(x) = -f(x)$

Solution

(A) Let $y = f(x) = \frac{3x+2}{5x-3}$.
Then $y(5x - 3) = 3x + 2$.
Expanding this,we get $5xy - 3y = 3x + 2$.
Rearranging the terms to solve for $x$,we have $5xy - 3x = 3y + 2$.
Factoring out $x$,we get $x(5y - 3) = 3y + 2$.
Thus,$x = \frac{3y+2}{5y-3}$.
By definition,$f^{-1}(y) = x = \frac{3y+2}{5y-3}$.
Replacing $y$ with $x$,we obtain $f^{-1}(x) = \frac{3x+2}{5x-3}$.
Since $f^{-1}(x) = f(x)$,the correct option is $A$.
105
EasyMCQ
If $g$ is the inverse of $f$ and $f^{\prime}(x)=\frac{1}{1+x^{2}}$,then $g^{\prime}(x)$ is equal to
A
$1+[g(x)]^{2}$
B
$\frac{-1}{1+[g(x)]^{2}}$
C
$\frac{1}{2(1+x^{2})}$
D
None of these

Solution

(A) Given that $g$ is the inverse of $f$,so $g(x) = f^{-1}(x)$.
This implies $f(g(x)) = x$.
Differentiating both sides with respect to $x$ using the chain rule,we get:
$f^{\prime}(g(x)) \cdot g^{\prime}(x) = 1$.
Therefore,$g^{\prime}(x) = \frac{1}{f^{\prime}(g(x))}$.
Given $f^{\prime}(x) = \frac{1}{1+x^{2}}$,we substitute $g(x)$ for $x$:
$f^{\prime}(g(x)) = \frac{1}{1+[g(x)]^{2}}$.
Substituting this into the expression for $g^{\prime}(x)$:
$g^{\prime}(x) = \frac{1}{\frac{1}{1+[g(x)]^{2}}} = 1 + [g(x)]^{2}$.
106
EasyMCQ
If $f: R \rightarrow R$ is a mapping defined by $f(x)=x^{3}+5$,then $f^{-1}(x)$ is equal to
A
$(x+5)^{1/3}$
B
$(x-5)^{1/3}$
C
$(5-x)^{1/3}$
D
$5-x$

Solution

(B) Let $y = f(x) = x^{3} + 5$.
To find the inverse,we express $x$ in terms of $y$:
$y - 5 = x^{3}$
$x = (y - 5)^{1/3}$
Since $f^{-1}(y) = x$,we have $f^{-1}(y) = (y - 5)^{1/3}$.
Replacing $y$ with $x$,we get $f^{-1}(x) = (x - 5)^{1/3}$.
107
DifficultMCQ
Let $f(x)=(x+1)^2-1, x \geqslant-1$,then the set $\{x : f(x)=f^{-1}(x)\}$ is
A
$\{0, 1, -1\}$
B
$\{0, -1\}$
C
$\{0, -1, \frac{-3+i \sqrt{3}}{2}, \frac{-3-i \sqrt{3}}{2}\}$
D
$\phi$

Solution

(B) Given $f(x) = (x+1)^2 - 1$ for $x \geqslant -1$.
Since $f(x)$ is an increasing function for $x \geqslant -1$,the solutions to $f(x) = f^{-1}(x)$ are the same as the solutions to $f(x) = x$.
Setting $f(x) = x$:
$(x+1)^2 - 1 = x$
$x^2 + 2x + 1 - 1 = x$
$x^2 + x = 0$
$x(x+1) = 0$
This gives $x = 0$ or $x = -1$.
Both values satisfy the condition $x \geqslant -1$.
Thus,the set is $\{0, -1\}$.
108
EasyMCQ
If $f: N \rightarrow N$ and $f(x) = x + 3$,then $f^{-1}(x) =$ . . . . . . .
A
$x + 3$
B
does not exist
C
$x - 3$
D
$3 - x$

Solution

(B) For a function $f: N \rightarrow N$ to have an inverse $f^{-1}$,the function must be a bijection (both one-one and onto).
Given $f(x) = x + 3$,where $N$ is the set of natural numbers.
For the function to be onto,the range must be equal to the codomain.
The range of $f(x) = x + 3$ for $x \in N$ is $\{4, 5, 6, \dots \}$.
The codomain is $N = \{1, 2, 3, 4, 5, 6, \dots \}$.
Since the range $\{4, 5, 6, \dots \} \neq N$,the function is not onto.
Therefore,$f^{-1}(x)$ does not exist.
109
EasyMCQ
If $f: R - \{\frac{3}{5}\} \rightarrow R - \{\frac{3}{5}\}$ is defined by $f(x) = \frac{3x+1}{5x-3}$,then which of the following is true?
A
$f^{-1}(x) = 2f(x)$
B
$f^{-1}(x) = f(x)$
C
$f^{-1}(x) = -f(x)$
D
$f^{-1}(x)$ does not exist

Solution

(B) To find the inverse of the function $f(x) = \frac{3x+1}{5x-3}$,let $y = f(x)$.
So,$y = \frac{3x+1}{5x-3}$.
Cross-multiplying gives $y(5x-3) = 3x+1$,which simplifies to $5xy - 3y = 3x + 1$.
Rearranging the terms to solve for $x$: $5xy - 3x = 3y + 1$.
Factoring out $x$: $x(5y - 3) = 3y + 1$.
Thus,$x = \frac{3y+1}{5y-3}$.
By definition,$f^{-1}(y) = x = \frac{3y+1}{5y-3}$.
Replacing $y$ with $x$,we get $f^{-1}(x) = \frac{3x+1}{5x-3}$.
Since $f^{-1}(x) = f(x)$,the correct option is $B$.
110
EasyMCQ
$f: R \rightarrow R, f(x) = 3x + 2$ and $g: R \rightarrow R, g(x) = 6x + 5$. Find the value of $(g \circ f^{-1})(10)$.
A
$21$
B
$29$
C
$7$
D
$\frac{8}{3}$

Solution

(A) Given $f(x) = 3x + 2$. Let $y = 3x + 2$,then $x = \frac{y - 2}{3}$.
Thus,$f^{-1}(y) = \frac{y - 2}{3}$,or $f^{-1}(x) = \frac{x - 2}{3}$.
We need to find $(g \circ f^{-1})(10) = g(f^{-1}(10))$.
First,calculate $f^{-1}(10) = \frac{10 - 2}{3} = \frac{8}{3}$.
Now,substitute this into $g(x) = 6x + 5$:
$g\left(\frac{8}{3}\right) = 6 \left(\frac{8}{3}\right) + 5 = 2(8) + 5 = 16 + 5 = 21$.
Therefore,the correct option is $A$.
111
EasyMCQ
$f: R \rightarrow R$,$f(x) = 4x + 3$ is defined,then $f^{-1}(x) =$ . . . . . . .
A
$\frac{x-3}{4}$
B
$\frac{x-4}{3}$
C
$\frac{x+3}{4}$
D
$\frac{x+4}{3}$

Solution

(A) To find the inverse function $f^{-1}(x)$,let $y = f(x)$.
Given $y = 4x + 3$.
Now,solve for $x$ in terms of $y$:
$y - 3 = 4x$
$x = \frac{y - 3}{4}$.
Since $f^{-1}(y) = x$,we have $f^{-1}(y) = \frac{y - 3}{4}$.
Replacing $y$ with $x$,we get $f^{-1}(x) = \frac{x - 3}{4}$.
Therefore,the correct option is $A$.
112
MediumMCQ
Let $f(x)=\sin 2x + \cos 2x$ and $g(x)=x^2-1$. Then $g(f(x))$ is invertible in the domain:
A
$x \in \left[\frac{-\pi}{8}, \frac{\pi}{8}\right]$
B
$x \in \left[\frac{-\pi}{2}, \frac{\pi}{2}\right]$
C
$x \in \left[0, \frac{\pi}{4}\right]$
D
$x \in \left[\frac{-\pi}{4}, \frac{\pi}{4}\right]$

Solution

(A) Given $f(x) = \sin 2x + \cos 2x$ and $g(x) = x^2 - 1$.
First,calculate the composite function $g(f(x))$:
$g(f(x)) = (\sin 2x + \cos 2x)^2 - 1$
$g(f(x)) = (\sin^2 2x + \cos^2 2x + 2 \sin 2x \cos 2x) - 1$
Since $\sin^2 \theta + \cos^2 \theta = 1$ and $2 \sin \theta \cos \theta = \sin 2\theta$:
$g(f(x)) = (1 + \sin 4x) - 1 = \sin 4x$.
$A$ function is invertible if it is one-to-one (injective) and onto (surjective) in the given domain.
The function $y = \sin \theta$ is invertible in the interval $\theta \in \left[\frac{-\pi}{2}, \frac{\pi}{2}\right]$.
Here,$\theta = 4x$,so we set:
$\frac{-\pi}{2} \le 4x \le \frac{\pi}{2}$
Dividing by $4$:
$\frac{-\pi}{8} \le x \le \frac{\pi}{8}$.
Thus,$g(f(x))$ is invertible in the domain $x \in \left[\frac{-\pi}{8}, \frac{\pi}{8}\right]$.
113
EasyMCQ
Let $f: R \rightarrow R$ be given by $f(x) = \tan x$. Then,$f^{-1}(1)$ is
A
$\frac{\pi}{4}$
B
$\{n \pi + \frac{\pi}{4} : n \in Z\}$
C
$\frac{\pi}{3}$
D
$\{n \pi + \frac{\pi}{3} : n \in Z\}$

Solution

(B) Given $f(x) = \tan x$.
The inverse function $f^{-1}(y)$ is defined such that $f(f^{-1}(y)) = y$.
Here,we need to find $f^{-1}(1)$,so we set $f(x) = 1$.
$\tan x = 1$.
The general solution for $\tan x = \tan \alpha$ is $x = n \pi + \alpha$,where $n \in Z$.
Since $\tan(\frac{\pi}{4}) = 1$,the set of values for $x$ is $\{n \pi + \frac{\pi}{4} : n \in Z\}$.
Therefore,$f^{-1}(1) = \{n \pi + \frac{\pi}{4} : n \in Z\}$.
114
EasyMCQ
Let $f: R \rightarrow R$ be defined by $f(x) = 2x + 6$,which is a bijective mapping. Then $f^{-1}(x)$ is given by:
A
$ \frac{x}{2} - 3 $
B
$ 2x + 6 $
C
$ x - 3 $
D
$ 6x + 2 $

Solution

(A) Given the function $f(x) = 2x + 6$,where $f: R \rightarrow R$.
To find the inverse $f^{-1}(x)$,let $y = f(x)$.
So,$y = 2x + 6$.
Solving for $x$ in terms of $y$:
$2x = y - 6$
$x = \frac{y - 6}{2}$
$x = \frac{y}{2} - 3$.
By definition,$f^{-1}(y) = x$,so $f^{-1}(y) = \frac{y}{2} - 3$.
Replacing $y$ with $x$,we get $f^{-1}(x) = \frac{x}{2} - 3$.
115
MediumMCQ
If $f: R \rightarrow R$ is defined by $f(x)=2x+3$,then $f^{-1}(x)$
A
is given by $\frac{x-3}{2}$
B
is given by $\frac{1}{2x+3}$
C
does not exist because $f$ is not injective
D
does not exist because $f$ is not surjective

Solution

(A) Let $x_{1}, x_{2} \in R$.
For injectivity,let $f(x_{1}) = f(x_{2})$.
$2x_{1} + 3 = 2x_{2} + 3$
$2x_{1} = 2x_{2}$
$x_{1} = x_{2}$.
Hence,$f$ is injective.
For surjectivity,let $y \in \text{codomain } R$.
Let $y = f(x) = 2x + 3$.
$y - 3 = 2x$
$x = \frac{y-3}{2}$.
Since for every $y \in R$,there exists an $x = \frac{y-3}{2} \in R$,$f$ is surjective.
Since $f$ is both injective and surjective,$f^{-1}$ exists.
Replacing $y$ with $x$,we get $f^{-1}(x) = \frac{x-3}{2}$.
116
EasyMCQ
If $f: R \rightarrow R$ is defined by $f(x)=x^{3}$,then $f^{-1}(8)$ is equal to
A
$\{2\}$
B
$\{2, 2\omega, 2\omega^{2}\}$
C
$\{2, -2\}$
D
$\{2, 2\}$

Solution

(A) Given the function $f(x) = x^{3}$.
To find $f^{-1}(8)$,we need to solve the equation $f(x) = 8$ for $x$.
$x^{3} = 8$
$x^{3} - 8 = 0$
$(x - 2)(x^{2} + 2x + 4) = 0$
This gives $x = 2$ as the real solution.
Since the domain of $f$ is $R$ (the set of real numbers),we only consider the real value.
Therefore,$f^{-1}(8) = \{2\}$.
117
EasyMCQ
If $f: R \rightarrow R$ is defined by $f(x)=|x|$,then
A
$f^{-1}(x)=-x$
B
$f^{-1}(x)=\frac{1}{|x|}$
C
the function $f^{-1}(x)$ does not exist
D
$f^{-1}(x)=\frac{1}{x}$

Solution

(C) We have $f(x) = |x|$.
For a function to be invertible,it must be both one-one (injective) and onto (surjective).
Consider the values $f(1) = |1| = 1$ and $f(-1) = |-1| = 1$.
Since $f(1) = f(-1)$ but $1 \neq -1$,the function is not one-one.
Because the function is not one-one,it is not bijective.
Therefore,the inverse function $f^{-1}(x)$ does not exist.
118
MediumMCQ
Suppose $f(x)=(x+1)^{2}$ for $x \geq -1$. If $g(x)$ is a function whose graph is the reflection of the graph of $f(x)$ in the line $y=x$,then $g(x) = $
A
$-\sqrt{x}-1$
B
$\sqrt{x}-1$
C
$\frac{1}{(x+1)^{2}}, x > -1$
D
$\sqrt{x}+1$

Solution

(B) Given that $f(x)=(x+1)^{2}$ for $x \geq -1$.
Since $g(x)$ is the reflection of the graph of $f(x)$ in the line $y=x$,$g(x)$ is the inverse function of $f(x)$,denoted as $f^{-1}(x)$.
To find the inverse,let $y = (x+1)^{2}$.
Since $x \geq -1$,we have $x+1 \geq 0$,so taking the square root of both sides gives $\sqrt{y} = x+1$.
Solving for $x$,we get $x = \sqrt{y} - 1$.
By interchanging $x$ and $y$,we obtain $f^{-1}(x) = \sqrt{x} - 1$.
Thus,$g(x) = \sqrt{x} - 1$.
119
MediumMCQ
If $f(x) = 2 + |\sin^{-1} x|$ and $A = \{x \in R : f^{-1}(x) \text{ exists} \}$,then $A = $
A
$\{0\}$
B
$[-1, 1]$
C
$(-\infty, -1) \cup (1, \infty)$
D
$(-1, 0) \cup (0, 1)$

Solution

(B) For $f^{-1}(x)$ to exist,the function $f(x)$ must be a bijection (both one-to-one and onto).
Given $f(x) = 2 + |\sin^{-1} x|$.
The domain of $\sin^{-1} x$ is $[-1, 1]$.
For $x \in [-1, 0]$,$f(x) = 2 - \sin^{-1} x$. This is a strictly decreasing function.
For $x \in [0, 1]$,$f(x) = 2 + \sin^{-1} x$. This is a strictly increasing function.
Since the function decreases on $[-1, 0]$ and increases on $[0, 1]$,it is not one-to-one on the interval $[-1, 1]$.
Specifically,$f(x_1) = f(x_2)$ for some $x_1 \in [-1, 0)$ and $x_2 \in (0, 1]$.
Therefore,$f(x)$ is not invertible on its entire domain $[-1, 1]$.
However,if the question implies the set $A$ where the inverse exists locally or is defined,typically such functions are not invertible. Given the options provided,there is no valid interval where the function is globally invertible. If we assume the question implies the domain where the function is defined,it is $[-1, 1]$. But strictly speaking,$f^{-1}(x)$ does not exist for the whole domain.
120
EasyMCQ
$f(x) = \sin x + \cos x, g(x) = x^2 - 1$. Then $g(f(x))$ is invertible if:
A
$-\frac{\pi}{4} \leq x \leq \frac{\pi}{4}$
B
$-\frac{\pi}{2} \leq x \leq 0$
C
$-\frac{\pi}{2} \leq x \leq \pi$
D
$0 \leq x \leq \frac{\pi}{2}$

Solution

(A) Given $f(x) = \sin x + \cos x$ and $g(x) = x^2 - 1$.
$g(f(x)) = g(\sin x + \cos x) = (\sin x + \cos x)^2 - 1$.
$= \sin^2 x + \cos^2 x + 2 \sin x \cos x - 1$.
$= 1 + \sin 2x - 1 = \sin 2x$.
For a function to be invertible,it must be one-one and onto in the given domain.
The function $h(x) = \sin 2x$ is one-one in the interval where the argument $2x$ lies within $[-\frac{\pi}{2}, \frac{\pi}{2}]$.
Thus,$-\frac{\pi}{2} \leq 2x \leq \frac{\pi}{2}$.
Dividing by $2$,we get $-\frac{\pi}{4} \leq x \leq \frac{\pi}{4}$.
Therefore,the function is invertible in the interval $[-\frac{\pi}{4}, \frac{\pi}{4}]$.
121
MediumMCQ
If $f(x) = (x+1)^2 - 1$ for $x \geq -1$,then find the set $\{x \mid f(x) = f^{-1}(x)\}$.
A
$\{0, -1\}$
B
$\{-1, 0, 1\}$
C
$\{-1, 0, \frac{-3 + \sqrt{3}i}{2}, \frac{-3 - \sqrt{3}i}{2}\}$
D
An empty set

Solution

(A) Given $f(x) = (x+1)^2 - 1$ for $x \geq -1$.
To find $f^{-1}(x)$,set $y = (x+1)^2 - 1$.
Then $y+1 = (x+1)^2$. Since $x \geq -1$,$x+1 = \sqrt{y+1}$,so $x = \sqrt{y+1} - 1$.
Thus,$f^{-1}(x) = \sqrt{x+1} - 1$.
The equation $f(x) = f^{-1}(x)$ is equivalent to $f(x) = x$ because $f$ is an increasing function for $x \geq -1$.
So,$(x+1)^2 - 1 = x$.
$x^2 + 2x + 1 - 1 = x$.
$x^2 + x = 0$.
$x(x+1) = 0$.
This gives $x = 0$ or $x = -1$.
Both values satisfy the condition $x \geq -1$.
Therefore,the set is $\{0, -1\}$.
122
EasyMCQ
If $g(x)$ is the inverse of the function $f(x)$ and $f^{\prime}(x) = \frac{1}{h(x)}$,then $g^{\prime}(x) = $
A
$h(g(x))$
B
$g(h(x))$
C
$h^{\prime}(f(x))$
D
$f(h(x))$

Solution

(A) Given that $g(x)$ is the inverse of the function $f(x)$,we have $f(g(x)) = x$.
By differentiating both sides with respect to $x$ using the chain rule,we get:
$f^{\prime}(g(x)) \cdot g^{\prime}(x) = 1$.
This implies $g^{\prime}(x) = \frac{1}{f^{\prime}(g(x))}$.
We are given $f^{\prime}(x) = \frac{1}{h(x)}$,which means $f^{\prime}(g(x)) = \frac{1}{h(g(x))}$.
Substituting this into the expression for $g^{\prime}(x)$:
$g^{\prime}(x) = \frac{1}{1 / h(g(x))} = h(g(x))$.
Thus,the correct option is $A$.
123
EasyMCQ
Let $f(x) = (x + 2)^2 - 2, x \geq - 2$. Then $f^{-1}(x) =$
A
$-\sqrt{2 + x} - 2$
B
$\sqrt{2 + x} + 2$
C
$\sqrt{2 + x} - 2$
D
$-\sqrt{2 + x} + 2$

Solution

(C) To find the inverse of the function $f(x) = (x + 2)^2 - 2$ for $x \geq -2$,we set $y = f(x)$.
$y = (x + 2)^2 - 2$
Add $2$ to both sides:
$y + 2 = (x + 2)^2$
Since $x \geq -2$,we have $x + 2 \geq 0$. Taking the positive square root of both sides:
$\sqrt{y + 2} = x + 2$
Subtract $2$ from both sides to solve for $x$:
$x = \sqrt{y + 2} - 2$
By definition,$f^{-1}(y) = \sqrt{y + 2} - 2$. Replacing $y$ with $x$,we get:
$f^{-1}(x) = \sqrt{x + 2} - 2$
124
MediumMCQ
The inverse of the function $y = \frac{10^x - 10^{-x}}{10^x + 10^{-x}}$ is
A
$\frac{1}{2} \log _{10}\left(\frac{1+x}{1-x}\right)$
B
$\frac{1}{2} \log _{10}\left(\frac{2+x}{2-x}\right)$
C
$\frac{1}{2} \log _{10}\left(\frac{1-x}{1+x}\right)$
D
$\frac{1}{2} \log _{10}\left(\frac{2-x}{2+x}\right)$

Solution

(A) Given the function $y = \frac{10^x - 10^{-x}}{10^x + 10^{-x}}$.
Multiply the numerator and denominator by $10^x$:
$y = \frac{10^{2x} - 1}{10^{2x} + 1}$
Now,solve for $x$ in terms of $y$:
$y(10^{2x} + 1) = 10^{2x} - 1$
$y \cdot 10^{2x} + y = 10^{2x} - 1$
$1 + y = 10^{2x} - y \cdot 10^{2x}$
$1 + y = 10^{2x}(1 - y)$
$10^{2x} = \frac{1 + y}{1 - y}$
Taking $\log_{10}$ on both sides:
$2x = \log_{10} \left( \frac{1 + y}{1 - y} \right)$
$x = \frac{1}{2} \log_{10} \left( \frac{1 + y}{1 - y} \right)$
Replacing $y$ with $x$ to find the inverse function $f^{-1}(x)$:
$f^{-1}(x) = \frac{1}{2} \log_{10} \left( \frac{1 + x}{1 - x} \right)$
125
MediumMCQ
If $[\cdot]$ denotes the greatest integer function and if $f:(5,10) \rightarrow(7,12)$ is a function defined by $f(x)=x+2\left[\frac{x}{5}\right]$,then
A
$f^{-1}(x)=x-1$
B
$f^{-1}(x)=x+2$
C
$f^{-1}(x)=x-2$
D
$f^{-1}(x) \text{ does not exist}$

Solution

(C) Given the function $f:(5,10) \rightarrow (7,12)$ defined by $f(x) = x + 2\left[\frac{x}{5}\right]$.
For $x \in (5, 10)$,the value of $\frac{x}{5}$ lies in the interval $(1, 2)$.
Therefore,the greatest integer function $\left[\frac{x}{5}\right] = 1$ for all $x \in (5, 10)$.
Substituting this into the function definition,we get $f(x) = x + 2(1) = x + 2$.
Since $f(x) = x + 2$ is a linear function,it is strictly increasing and therefore one-to-one (injective).
To check if it is onto (surjective),we find the range: as $x$ varies from $5$ to $10$,$f(x)$ varies from $5+2=7$ to $10+2=12$. Thus,the range is $(7, 12)$,which matches the codomain.
Since $f$ is bijective,$f^{-1}(x)$ exists.
Let $y = x + 2$,then $x = y - 2$.
Thus,$f^{-1}(x) = x - 2$.
126
MediumMCQ
If $f: R \rightarrow R$ and $g: R \rightarrow R$ are defined by $f(x) = 5x - 3$ and $g(x) = x^2 + 3$,then $g \circ f^{-1}(3)$ is equal to
A
$\frac{25}{3}$
B
$\frac{111}{25}$
C
$\frac{9}{25}$
D
$\frac{25}{111}$

Solution

(B) Given,$f(x) = 5x - 3$ and $g(x) = x^2 + 3$.
To find $f^{-1}(x)$,let $y = f(x) = 5x - 3$.
Then $y + 3 = 5x$,which implies $x = \frac{y + 3}{5}$.
Thus,$f^{-1}(y) = \frac{y + 3}{5}$,so $f^{-1}(x) = \frac{x + 3}{5}$.
Now,we need to calculate $g \circ f^{-1}(3) = g(f^{-1}(3))$.
First,find $f^{-1}(3) = \frac{3 + 3}{5} = \frac{6}{5}$.
Then,$g(\frac{6}{5}) = (\frac{6}{5})^2 + 3 = \frac{36}{25} + 3$.
Calculating the sum: $\frac{36 + 75}{25} = \frac{111}{25}$.
127
DifficultMCQ
If the functions $f$ and $g$ are defined by $f(x) = 3x - 4$ and $g(x) = 2 + 3x$ for $x \in R$,then $g^{-1}(f^{-1}(5))$ is equal to
A
$1$
B
$\frac{1}{2}$
C
$\frac{1}{3}$
D
$\frac{1}{4}$

Solution

(C) Given functions are $f(x) = 3x - 4$ and $g(x) = 3x + 2$.
To find $f^{-1}(y)$,let $f(x) = y$.
$3x - 4 = y \implies 3x = y + 4 \implies x = \frac{y + 4}{3}$.
Thus,$f^{-1}(y) = \frac{y + 4}{3}$.
Now,$f^{-1}(5) = \frac{5 + 4}{3} = \frac{9}{3} = 3$.
To find $g^{-1}(z)$,let $g(x) = z$.
$3x + 2 = z \implies 3x = z - 2 \implies x = \frac{z - 2}{3}$.
Thus,$g^{-1}(z) = \frac{z - 2}{3}$.
Finally,$g^{-1}(f^{-1}(5)) = g^{-1}(3) = \frac{3 - 2}{3} = \frac{1}{3}$.
128
MediumMCQ
If $g$ is the inverse of the function $f(x)$ and $g(x) = x + \tan x$,then $f^{\prime}(x) = $
A
$1 + \sec^2 x$
B
$\frac{1}{1 + \sec^2 f(x)}$
C
$\frac{1}{1 + \sec^2 g(x)}$
D
$1 + \sec^2 f(x)$

Solution

(B) Given that $g(x)$ is the inverse of $f(x)$,we have $f(g(x)) = x$.
Differentiating both sides with respect to $x$ using the chain rule,we get $f^{\prime}(g(x)) \cdot g^{\prime}(x) = 1$.
Therefore,$f^{\prime}(g(x)) = \frac{1}{g^{\prime}(x)}$.
Given $g(x) = x + \tan x$,we find $g^{\prime}(x) = 1 + \sec^2 x$.
Substituting this into the expression,we get $f^{\prime}(g(x)) = \frac{1}{1 + \sec^2 x}$.
Let $y = g(x)$,then $x = f(y)$.
Substituting $x = f(y)$ into the equation,we get $f^{\prime}(y) = \frac{1}{1 + \sec^2(f(y))}$.
Replacing $y$ with $x$,we obtain $f^{\prime}(x) = \frac{1}{1 + \sec^2(f(x))}$.
129
MediumMCQ
Let $f: R \rightarrow R$ and $g: R \rightarrow R$ be differentiable functions such that $(f \circ g)(x) = x$. If $f(x) = 2x + \cos x + \sin^2 x$,then the value of $\sum_{n=1}^{99} g(1 + (2n - 1) \pi)$ is
A
$1250 \pi$
B
$(99)^2 \frac{\pi}{2}$
C
$(99)^2 \pi$
D
$2500 \pi$

Solution

(B) Given $(f \circ g)(x) = x$,$g(x)$ is the inverse function of $f(x)$.
Let $g(1 + (2n - 1) \pi) = x_n$. Then $f(x_n) = 1 + (2n - 1) \pi$.
Substituting $f(x) = 2x + \cos x + \sin^2 x$:
$2x_n + \cos x_n + \sin^2 x_n = 1 + (2n - 1) \pi$
$2x_n + \cos x_n + 1 - \cos^2 x_n = 1 + (2n - 1) \pi$
$2x_n + \cos x_n - \cos^2 x_n = (2n - 1) \pi$.
For $x_n = (2n - 1) \frac{\pi}{2}$,we have $\cos x_n = 0$.
Substituting this into the equation: $2((2n - 1) \frac{\pi}{2}) + 0 - 0 = (2n - 1) \pi$,which holds true.
Thus,$g(1 + (2n - 1) \pi) = (2n - 1) \frac{\pi}{2}$.
Now,$\sum_{n=1}^{99} g(1 + (2n - 1) \pi) = \sum_{n=1}^{99} (2n - 1) \frac{\pi}{2} = \frac{\pi}{2} \sum_{n=1}^{99} (2n - 1)$.
The sum of the first $99$ odd numbers is $99^2$.
Therefore,the sum is $(99)^2 \frac{\pi}{2}$.
130
MediumMCQ
The inverse of the function $y = \frac{10^x - 10^{-x}}{10^x + 10^{-x}} + 1$ is $x =$
A
$\log \left(\frac{y}{2-y}\right)$
B
$\log_{10} \left(\frac{y}{2-y}\right)$
C
$\frac{1}{10} \log \left(\frac{y}{1-y}\right)$
D
$\frac{1}{2} \log_{10} \left(\frac{y}{2-y}\right)$

Solution

(D) Given the function $y = \frac{10^x - 10^{-x}}{10^x + 10^{-x}} + 1$.
Subtract $1$ from both sides: $y - 1 = \frac{10^x - 10^{-x}}{10^x + 10^{-x}}$.
Let $u = 10^x$. Then $10^{-x} = \frac{1}{u}$.
So,$y - 1 = \frac{u - 1/u}{u + 1/u} = \frac{u^2 - 1}{u^2 + 1}$.
Let $Y = y - 1$. Then $Y(u^2 + 1) = u^2 - 1$.
$Yu^2 + Y = u^2 - 1 \implies Y + 1 = u^2(1 - Y)$.
$u^2 = \frac{1 + Y}{1 - Y} = \frac{1 + (y - 1)}{1 - (y - 1)} = \frac{y}{2 - y}$.
Since $u = 10^x$,we have $10^{2x} = \frac{y}{2 - y}$.
Taking $\log_{10}$ on both sides: $2x = \log_{10} \left(\frac{y}{2 - y}\right)$.
Therefore,$x = \frac{1}{2} \log_{10} \left(\frac{y}{2 - y}\right)$.
131
EasyMCQ
Let $f: A \rightarrow B$ and $g: B \rightarrow A$ be defined as $f(x)=x^2 \forall x \in A$ and $g(x)=x^{1/2} \forall x \in B$. $f(x)$ and $g(x)$ are inverse functions to each other when
A
$A=B=R$
B
$A=R \setminus R^{-}; B=R \setminus R^{+}$
C
$A=R; B=R \setminus R^{-}$
D
$A=B=R \setminus R^{-}$

Solution

(D) For two functions $f: A \rightarrow B$ and $g: B \rightarrow A$ to be inverses of each other,they must satisfy $g(f(x)) = x$ for all $x \in A$ and $f(g(x)) = x$ for all $x \in B$.
Given $f(x) = x^2$ and $g(x) = x^{1/2}$.
For $g(x) = \sqrt{x}$ to be defined,we must have $x \geq 0$ for all $x \in B$. Thus,$B = [0, \infty) = R \setminus R^{-}$.
For $f(g(x)) = (x^{1/2})^2 = x$,this holds for all $x \in B$.
For $g(f(x)) = (x^2)^{1/2} = |x|$,we require $|x| = x$,which implies $x \geq 0$. Thus,$A = [0, \infty) = R \setminus R^{-}$.
Therefore,$f(x)$ and $g(x)$ are inverse functions to each other when $A = B = R \setminus R^{-}$.
132
EasyMCQ
If a function $f:(-1,1) \rightarrow B(\subseteq R)$ is defined as $f(x)=x+x^2+x^3+\ldots \infty$,then in order to have the inverse function of $f$,$B$ is equal to
A
$\left(-\infty, \frac{1}{2}\right)$
B
$\left(-\frac{1}{2}, \infty\right)$
C
$(-1, 1)$
D
$R$

Solution

(B) Given,$f(x) = x + x^2 + x^3 + \ldots \infty$.
This is an infinite geometric series with first term $a = x$ and common ratio $r = x$.
Since the domain is $(-1, 1)$,$|x| < 1$,the sum is given by $f(x) = \frac{x}{1-x}$.
To find the range $B$,we set $y = \frac{x}{1-x}$.
$y(1-x) = x \Rightarrow y - xy = x \Rightarrow y = x(1+y) \Rightarrow x = \frac{y}{1+y}$.
Since $-1 < x < 1$,we have $-1 < \frac{y}{1+y} < 1$.
Case $1$: $\frac{y}{1+y} > -1 \Rightarrow \frac{y + 1 + y}{1+y} > 0 \Rightarrow \frac{2y+1}{1+y} > 0$.
Critical points are $y = -1$ and $y = -1/2$. Testing intervals,we get $y \in (-\infty, -1) \cup (-1/2, \infty)$.
Case $2$: $\frac{y}{1+y} < 1 \Rightarrow \frac{y - 1 - y}{1+y} < 0 \Rightarrow \frac{-1}{1+y} < 0 \Rightarrow \frac{1}{1+y} > 0 \Rightarrow y > -1$.
Taking the intersection of Case $1$ and Case $2$,we get $y \in (-1/2, \infty)$.
Thus,$B = (-1/2, \infty)$.
133
EasyMCQ
If $\alpha$ is the minimum value for which the inverse of $f(x)=x^2+3x-3$ exists in $[\alpha, \infty)$ and $g$ is the inverse of $f$,then find the value of $\frac{dg}{dx}$ at $x=\alpha+\frac{5}{2}$.
A
$\frac{1}{2}$
B
$\frac{1}{3}$
C
$\frac{1}{4}$
D
$\frac{1}{5}$

Solution

(D) Given $f(x) = x^2 + 3x - 3$.
Completing the square,we get $f(x) = (x + \frac{3}{2})^2 - \frac{9}{4} - 3 = (x + \frac{3}{2})^2 - \frac{21}{4}$.
For the inverse to exist,the function must be monotonic. The vertex of the parabola is at $x = -\frac{3}{2}$,so the function is strictly increasing on $[-\frac{3}{2}, \infty)$. Thus,$\alpha = -\frac{3}{2}$.
Let $y = (x + \frac{3}{2})^2 - \frac{21}{4}$. Then $x + \frac{3}{2} = \sqrt{y + \frac{21}{4}}$,so $g(x) = f^{-1}(x) = \sqrt{x + \frac{21}{4}} - \frac{3}{2}$.
We need to find $g'(x)$ at $x = \alpha + \frac{5}{2} = -\frac{3}{2} + \frac{5}{2} = 1$.
$g'(x) = \frac{d}{dx}(\sqrt{x + \frac{21}{4}} - \frac{3}{2}) = \frac{1}{2\sqrt{x + \frac{21}{4}}}$.
At $x = 1$,$g'(1) = \frac{1}{2\sqrt{1 + \frac{21}{4}}} = \frac{1}{2\sqrt{\frac{25}{4}}} = \frac{1}{2 \times \frac{5}{2}} = \frac{1}{5}$.
134
DifficultMCQ
Let $f(x)=(x+1)^2-1, x \geq-1$. Then $\{x \mid f(x)=f^{-1}(x)\} =$
A
$\{0, 1, -1\}$
B
$\{-1, \frac{-3+i \sqrt{3}}{2}, \frac{-3-i \sqrt{3}}{2}\}$
C
$\{0, -1\}$
D
$\phi$

Solution

(C) Given $f(x) = (x+1)^2 - 1$ for $x \geq -1$.
To find $f^{-1}(x)$,set $y = (x+1)^2 - 1$.
Then $y+1 = (x+1)^2$,so $x+1 = \sqrt{y+1}$ (since $x \geq -1$),which gives $x = \sqrt{y+1} - 1$.
Thus,$f^{-1}(x) = \sqrt{x+1} - 1$.
We solve $f(x) = f^{-1}(x)$,which implies $(x+1)^2 - 1 = \sqrt{x+1} - 1$.
This simplifies to $(x+1)^2 = \sqrt{x+1}$.
Squaring both sides,we get $(x+1)^4 = x+1$,or $(x+1)((x+1)^3 - 1) = 0$.
This gives $x+1 = 0$ or $(x+1)^3 = 1$.
Case $1$: $x+1 = 0 \Rightarrow x = -1$.
Case $2$: $x+1 = 1 \Rightarrow x = 0$.
Case $3$: $x+1 = \omega$ or $x+1 = \omega^2$,where $\omega$ is a complex cube root of unity.
$x = \omega - 1 = \frac{-1+i\sqrt{3}}{2} - 1 = \frac{-3+i\sqrt{3}}{2}$ and $x = \omega^2 - 1 = \frac{-1-i\sqrt{3}}{2} - 1 = \frac{-3-i\sqrt{3}}{2}$.
Since the domain is $x \geq -1$,we only consider real values $x = -1$ and $x = 0$.
Thus,the set is $\{0, -1\}$.
135
EasyMCQ
If $f:[1, \infty) \rightarrow [0, \infty)$ is given by $f(x) = x - \frac{1}{x}$,then $f^{-1}(x) =$
A
$\frac{x+\sqrt{x^2+4}}{2}$
B
$\frac{x}{x^2-1}$
C
$\frac{1}{2}\left[x+\sqrt{x^2+4}\right]$
D
$\frac{1}{2}\left[x-\sqrt{x^2+4}\right]$

Solution

(C) Given $f(x) = x - \frac{1}{x}$. Let $y = f(x)$,so $y = x - \frac{1}{x}$.
To find $f^{-1}(x)$,we solve for $x$ in terms of $y$:
$y = \frac{x^2 - 1}{x} \Rightarrow x^2 - yx - 1 = 0$.
Using the quadratic formula $x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$:
$x = \frac{y \pm \sqrt{y^2 - 4(1)(-1)}}{2(1)} = \frac{y \pm \sqrt{y^2 + 4}}{2}$.
Since the domain of $f$ is $[1, \infty)$,$x$ must be positive,so we take the positive root:
$x = \frac{y + \sqrt{y^2 + 4}}{2}$.
Replacing $y$ with $x$,we get $f^{-1}(x) = \frac{x + \sqrt{x^2 + 4}}{2}$.
136
EasyMCQ
If $f:[1, \infty) \rightarrow [1, \infty)$ is defined by $f(x) = \frac{1+\sqrt{1+4 \log_2 x}}{2}$,then $f^{-1}(3) =$
A
$0$
B
$1$
C
$64$
D
$\frac{1+\sqrt{5}}{2}$

Solution

(C) Given $f(x) = \frac{1+\sqrt{1+4 \log_2 x}}{2}$.
To find $f^{-1}(3)$,we set $f(x) = y$,which implies $x = f^{-1}(y)$.
$\frac{1+\sqrt{1+4 \log_2 x}}{2} = y$
$\sqrt{1+4 \log_2 x} = 2y - 1$
Squaring both sides:
$1 + 4 \log_2 x = (2y - 1)^2$
$1 + 4 \log_2 x = 4y^2 - 4y + 1$
$4 \log_2 x = 4y^2 - 4y$
$\log_2 x = y^2 - y$
$x = 2^{y^2 - y}$
Thus,$f^{-1}(y) = 2^{y^2 - y}$.
Now,substitute $y = 3$:
$f^{-1}(3) = 2^{3^2 - 3}$
$f^{-1}(3) = 2^{9 - 3}$
$f^{-1}(3) = 2^6 = 64$.
137
MediumMCQ
Let $x \neq 0$ and $|x| < \frac{1}{2}$. If $f(x) = 1 + 2x + 4x^2 + 8x^3 + \ldots$,then $f^{-1}(x) =$
A
$\frac{x-1}{2x}$
B
$\frac{x-1}{2}$
C
$\frac{x-1}{x}$
D
$1-2x$

Solution

(A) Given the function $f(x) = 1 + 2x + 4x^2 + 8x^3 + \ldots$ for $|x| < \frac{1}{2}$.
This is an infinite geometric series with first term $a = 1$ and common ratio $r = 2x$.
The sum of an infinite geometric series is given by $S_{\infty} = \frac{a}{1-r}$.
Thus,$f(x) = \frac{1}{1-2x}$.
Let $y = f(x) = \frac{1}{1-2x}$.
To find $f^{-1}(x)$,we solve for $x$ in terms of $y$:
$y(1-2x) = 1$
$y - 2xy = 1$
$2xy = y - 1$
$x = \frac{y-1}{2y}$.
Replacing $y$ with $x$,we get $f^{-1}(x) = \frac{x-1}{2x}$.
138
MediumMCQ
If $f:[1, \infty) \rightarrow[5, \infty)$ is given by $f(x)=3x+\frac{2}{x}$,then $f^{-1}(x)=$
A
$\frac{1}{6}\left[x+\sqrt{x^2-24}\right]$
B
$\frac{x}{3x^2+2}$
C
$\frac{1}{6}\left[x-\sqrt{x^2-24}\right]$
D
$\frac{1}{2}\left[1+\sqrt{x^2-4}\right]$

Solution

(A) Given $f(x) = 3x + \frac{2}{x}$. Let $y = 3x + \frac{2}{x}$.
Multiplying by $x$,we get $3x^2 - yx + 2 = 0$.
Using the quadratic formula,$x = \frac{y \pm \sqrt{y^2 - 4(3)(2)}}{2(3)} = \frac{y \pm \sqrt{y^2 - 24}}{6}$.
Since the domain is $x \in [1, \infty)$,we must choose the root that satisfies this condition.
For $y \geq 5$,$y^2 \geq 25$,so $\sqrt{y^2 - 24} \geq 1$.
If we take $x = \frac{y - \sqrt{y^2 - 24}}{6}$,then for $y=5$,$x = \frac{5 - 1}{6} = \frac{2}{3} < 1$,which is outside the domain.
If we take $x = \frac{y + \sqrt{y^2 - 24}}{6}$,then for $y=5$,$x = \frac{5 + 1}{6} = 1$,which is in the domain.
Thus,$f^{-1}(x) = \frac{x + \sqrt{x^2 - 24}}{6}$.
139
EasyMCQ
$f: (-\infty, 0] \rightarrow [0, \infty)$ is defined as $f(x) = x^2$. The domain and range of its inverse are
A
Domain of $f^{-1} = [0, \infty)$,Range of $f^{-1} = (-\infty, 0]$
B
Domain of $f^{-1} = [0, \infty)$,Range of $f^{-1} = (-\infty, \infty)$
C
Domain of $f^{-1} = [0, \infty)$,Range of $f^{-1} = (0, \infty)$
D
$f^{-1}$ does not exist

Solution

(A) We have a function $f: (-\infty, 0] \rightarrow [0, \infty)$ defined as $f(x) = x^2$.
Since each line parallel to the $x$-axis cuts the curve at most at one point,the function $f$ is one-one.
From the graph,it is clear that the range of $f$ is $[0, \infty)$,which is equal to the codomain.
Therefore,$f$ is onto.
Since $f$ is both one-one and onto,it is invertible.
The inverse function $f^{-1}$ maps the codomain of $f$ to the domain of $f$.
Thus,$f^{-1}: [0, \infty) \rightarrow (-\infty, 0]$.
Hence,the domain of $f^{-1}$ is $[0, \infty)$ and the range of $f^{-1}$ is $(-\infty, 0]$.
Solution diagram
140
EasyMCQ
Let $f$ and $g$ be two differentiable functions satisfying $g^{\prime}(5)=\frac{3}{4}$,$g(5)=6$ and $g=f^{-1}$. Then $f^{\prime}(6)$ is equal to
A
$\frac{1}{2}$
B
$\frac{1}{6}$
C
$\frac{2}{3}$
D
$\frac{4}{3}$

Solution

(D) Given that $g(x) = f^{-1}(x)$.
By the definition of inverse functions,we have $f(g(x)) = x$.
Differentiating both sides with respect to $x$ using the chain rule,we get $f^{\prime}(g(x)) \cdot g^{\prime}(x) = 1$.
Therefore,$f^{\prime}(g(x)) = \frac{1}{g^{\prime}(x)}$.
We are given $g(5) = 6$ and $g^{\prime}(5) = \frac{3}{4}$.
Substituting $x = 5$ into the equation $f^{\prime}(g(x)) = \frac{1}{g^{\prime}(x)}$,we get $f^{\prime}(g(5)) = \frac{1}{g^{\prime}(5)}$.
Since $g(5) = 6$,this becomes $f^{\prime}(6) = \frac{1}{g^{\prime}(5)}$.
Substituting the value $g^{\prime}(5) = \frac{3}{4}$,we get $f^{\prime}(6) = \frac{1}{3/4} = \frac{4}{3}$.
141
MediumMCQ
Consider the function $y = \log_{a}(x + \sqrt{x^{2} + 1})$ where $a > 0$ and $a \neq 1$. The inverse of the function:
A
does not exist
B
is $x = \log_{1/a}(y + \sqrt{y^{2} + 1})$
C
is $x = \sinh(y \log a)$
D
is $x = \cosh(-y \log \frac{1}{a})$

Solution

(C) Given,$y = \log_{a}(x + \sqrt{x^{2} + 1})$,$a > 0, a \neq 1$.
Taking exponential on both sides,we get $a^{y} = x + \sqrt{x^{2} + 1}$.
Now,consider $a^{-y} = \frac{1}{x + \sqrt{x^{2} + 1}}$.
Rationalizing the denominator,we get $a^{-y} = \sqrt{x^{2} + 1} - x$.
Subtracting the two equations: $a^{y} - a^{-y} = (x + \sqrt{x^{2} + 1}) - (\sqrt{x^{2} + 1} - x) = 2x$.
Thus,$x = \frac{a^{y} - a^{-y}}{2}$.
Since $a^{y} = e^{y \ln a}$,we have $x = \frac{e^{y \ln a} - e^{-y \ln a}}{2}$.
Using the definition $\sinh(u) = \frac{e^{u} - e^{-u}}{2}$,we get $x = \sinh(y \ln a)$.
Therefore,the inverse function is $f^{-1}(y) = \sinh(y \log a)$.
142
MediumMCQ
Let $f(x) > 0$ for all $x$ and $f^{\prime}(x)$ exists for all $x$. If $f$ is the inverse function of $h$ and $h^{\prime}(x) = \frac{1}{1 + \log x}$,then $f^{\prime}(x)$ will be
A
$1 + \log (f(x))$
B
$1 + f(x)$
C
$1 - \log (f(x))$
D
$\log f(x)$

Solution

(A) Given that $f$ is the inverse function of $h$,we have $h(f(x)) = x$.
Differentiating both sides with respect to $x$ using the chain rule:
$h^{\prime}(f(x)) \cdot f^{\prime}(x) = 1$
Therefore,$f^{\prime}(x) = \frac{1}{h^{\prime}(f(x))}$.
Given $h^{\prime}(x) = \frac{1}{1 + \log x}$,we substitute $f(x)$ for $x$ to get $h^{\prime}(f(x)) = \frac{1}{1 + \log(f(x))}$.
Substituting this into the expression for $f^{\prime}(x)$:
$f^{\prime}(x) = \frac{1}{\frac{1}{1 + \log(f(x))}} = 1 + \log(f(x))$.
143
MediumMCQ
If $f$ is the inverse function of $g$ and $g^{\prime}(x)=\frac{1}{1+x^n}$,then the value of $f^{\prime}(x)$ is
A
$1+\{f(x)\}^n$
B
$1-\{f(x)\}^n$
C
$\{1+f(x)\}^n$
D
$\{f(x)\}^n$

Solution

(A) Given that $f$ is the inverse function of $g$,we have $f(x) = g^{-1}(x)$.
We know that the derivative of an inverse function is given by the formula: $f^{\prime}(x) = \frac{1}{g^{\prime}(f(x))}$.
Given $g^{\prime}(x) = \frac{1}{1+x^n}$,we substitute $f(x)$ for $x$ in the expression for $g^{\prime}(x)$:
$g^{\prime}(f(x)) = \frac{1}{1+\{f(x)\}^n}$.
Now,substitute this into the formula for $f^{\prime}(x)$:
$f^{\prime}(x) = \frac{1}{\frac{1}{1+\{f(x)\}^n}} = 1+\{f(x)\}^n$.

Relation and Function — Inverse Function · Frequently Asked Questions

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Yes. All questions in this section are mapped to JEE Main and NEET exam patterns. Previous year questions from JEE Main, NEET, GUJCET and state-level exams are included with full solutions.

2Can I switch to Hindi or Gujarati for these questions?

Yes. Use the language tabs in the hero section or the sidebar to view the same questions and solutions in English, Hindi or Gujarati.

3How do I generate a question paper from this subtopic?

Use the Vedclass Exam Paper Generator — select the chapter and subtopic, set difficulty, and generate Sets A, B, C, D automatically. First 3 chapters of every subject are free.

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