Trigonometric Functions — Maths STD 12 Science — Question

$

\therefore \quad \cos 2 \theta=\cos \frac{3 \pi}{4}\left(\text { As cos } \frac{\pi}{4}=\frac{1}{\sqrt{2}} \text { and } \cos (\pi-A)=\cos A\right)

$

The general solution of $\cos \theta=\cos \alpha$ is $\theta=2 n \pi \pm \alpha$, where $n \in Z$.

$\therefore \quad$ The general solution of $\cos 2 \theta=\cos \frac{3 \pi}{4}$ is $2 \theta=2 n \pi \pm \frac{3 \pi}{4}$, where $n \in Z$.

$\therefore \quad$ The general solution of $\cos 2 \theta=-\frac{1}{\sqrt{2}}$ is $\theta=n \pi \pm \frac{3 \pi}{8}$, where $n \in Z$.