Find the general solution of the equation $\cos 3 x+\cos x-\cos 2 x=0$

Vedclass pdf generator app on play store
Vedclass iOS app on app store

$\cos 3 x+\cos x-\cos 2 x=0$

$ \Rightarrow 2\cos \left( {\frac{{3x + 2}}{2}} \right)\cos \left( {\frac{{3x - x}}{2}} \right) - \cos 2x = 0\quad $

$\left[ {\cos A + \cos B = 2\cos \left( {\frac{{A + B}}{2}} \right)\cos \left( {\frac{{A - B}}{2}} \right)} \right]$

$\Rightarrow 2 \cos 2 x \cos x-\cos 2 x=0$

$\Rightarrow \cos 2 x(2 \cos x-1)=0$

$\Rightarrow \cos 2 x=0 \quad$ or $\quad 2 \cos x-1=0$

$\Rightarrow \cos 2 x=0 \quad$ or $\quad \cos x=\frac{1}{2}$

$\therefore 2 x=(2 n+1) \frac{\pi}{2}$

or $\quad \cos x=\cos \frac{\pi}{3},$ where $n \in Z$

$\Rightarrow x=(2 n+1) \frac{\pi}{4}$

or $\quad x=2 n \pi \pm \frac{\pi}{3},$ where $n \in Z$

Similar Questions

Solve $2 \cos ^{2} x+3 \sin x=0$

If $\cos \theta + \cos 7\theta + \cos 3\theta + \cos 5\theta = 0$, then $\theta $

If the solution for $\theta $ of $\cos p\theta + \cos q\theta = 0,\;p > 0,\;q > 0$ are in $A.P.$, then the numerically smallest common difference of $A.P.$ is

If $\cos \theta + \cos 2\theta + \cos 3\theta = 0$, then the general value of $\theta $ is

For $n \in Z$ , the general solution of the equation

$(\sqrt 3  - 1)\,\sin \,\theta \, + \,(\sqrt 3  + 1)\,\cos \theta \, = \,2$ is