Question

Найдите значение выражения
7√2 cos^2 5π8-7√2 sin^2 5π8

Answer 1

$7 sqrt{2}cos^{2}( frac{5 pi }{8}) -7 sqrt{2}sin^{2}( frac{5 pi }{8})=7 sqrt{2}*cos(2* frac{5 pi }{8})=$$7 sqrt{2}*cos(frac{10 pi }{8})=7 sqrt{2}*cos( pi +frac{ pi }{4})=-7 sqrt{2}*cos(frac{ pi }{4})=-7 sqrt{2}*frac{sqrt{2}}{2}=-7$