Question

5 корней из 2 * sin 7пи/8 * cos 7пи/8

Answer 1

$5\sqrt2\cdot sin\frac{7\pi}{8}\cdot cos\frac{7\pi}{8}=5\sqrt2\cdot \frac{1}{2}\cdot (2sin\frac{7\pi}{8}\cdot cos\frac{7\pi}{8})=\frac{5\sqrt2}{2}\cdot sin(2\cdot \frac{7\pi}{8})=\\\\=\frac{5\sqrt2}{2}\cdot sin\frac{7\pi}{4}=\frac{5\sqrt2}{2}\cdot (-\frac{\sqrt2}{2})=-2,5$