Question

Вычислите:
2($cos^{2} \frac{\pi }{8}-sin^{2}\frac{\pi }{8}$)

Answer 1

$2( {cos}^{2} \frac{\pi}{8} - {sin}^{2} \frac{\pi}{8} ) = 2cos(2 \times \frac{\pi}{8} ) = 2cos \frac{\pi}{4} = 2 \times \frac{ \sqrt{2} }{2} = \sqrt{2}$