Question

Find the principal solution of $3co{s}^2\theta -cos2\theta =1$

• A. $\theta =0$
• B. $\theta =-\frac{\pi }{2}$
• C. $\theta =\frac{\pi }{2}$
• D. $\theta =\pi$

Answer 1

The correct option is C

$\theta =\frac{\pi }{2}$

$3co{s}^2\theta -cos2\theta =13co{s}^2\theta -(2co{s}^2\theta -1)=1co{s}^2\theta =0cos\theta =0\theta =\frac{\pi }{2}$