Question

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

• A. $\cos 2\theta(2\cos\theta + 1) = 0$
• B. $\cos 2\theta = 0 = \cos\frac{\pi}{2}$
• C. $\theta = \frac{\pi}{4}$
• D. $\theta = 2m\pi \pm \frac{\pi}{4}$

Answer 1

Answer: (D)

$\theta = 2m\pi \pm \frac{\pi}{4}$

Answer 2

$\Rightarrow$

$2A = 2n\pi + \frac{\pi}{2} \Rightarrow$.