Question

Помогите решить при a=П/12

Answer 1

$1 - 2 {cos}^{2} ( \frac{\pi}{2} + \frac{\pi}{12}) = \\ = 1 + 2 {sin}^{2} \frac{\pi}{12} = \\ = 1+2 \times \frac{1 - cos( \frac{2\pi}{12} )}{2} = \\ = 2 - cos( \frac{\pi}{6} ) = \\ = 2 - \frac{ \sqrt{3} }{2} = \frac{ \sqrt{13} }{2}$