Question

2 косинус в квадрате х пи /8-1=

Answer 1

$2cos^2 \frac{\pi}{8} -1=2\bullet\frac{1+cos\frac{\pi}{4}}{2}-1=1+cos\frac{\pi}{4}-1=cos\frac{\pi}{4}=\frac{\sqrt{2}}{2}.$