Mathematics

Problem

The number of solutions of the equation

\cos 2\theta \cos \frac{\theta}{2} + \cos \frac{5\theta}{2} = 2 \cos^3 \frac{5\theta}{2} \text{ in } \left[-\frac{\pi}{2}, \frac{\pi}{2}\right] \text{ is :}

[April 7, 2025 (II)] (a) 7 (b) 5 (c) 6 (d) 9