(D) The function $f(n)$ represents the sum of all positive divisors of $n$. For a number $n = 2^k \cdot 3^1$,the divisors are the products of the divi

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(D) The function $f(n)$ represents the sum of all positive divisors of $n$. For a number $n = 2^k \cdot 3^1$,the divisors are the products of the divisors of $2^k$ and the divisors of $3^1$. The sum of divisors of $2^k$ is $(1 + 2 + 2^2 + \dots + 2^k) = \frac{2^{k+1}-1}{2-1} = 2^{k+1}-1$. The sum of divisors of $3^1$ is $(1 + 3) = 4$. Since $f$ is a multiplicative function for coprime factors,$f(2^k \cdot 3) = f(2^k) \cdot f(3)$. Thus,$f(2^k \cdot 3) = (2^{k+1}-1) \cdot 4 = 4(2^{k+1}-1)$.

Class 12 Mathematics Relation and Function Mix Examples of Relation and Function

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If $N$ denotes the set of all positive integers and if $f: N \rightarrow N$ is defined by $f(n) = \text{the sum of positive divisors of } n$,then $f(2^k \cdot 3)$,where $k$ is a positive integer,is

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A
$2^{k+1}-1$
B
$2(2^{k+1}-1)$
C
$3(2^{k+1}-1)$
D
$4(2^{k+1}-1)$

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If $N$ denotes the set of all positive integers and if $f: N \rightarrow N$ is defined by $f(n) = \text{the sum of positive divisors of } n$,then $f(2^k \cdot 3)$,where $k$ is a positive integer,is

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