Question

Упростить выражение -4cos^2 a+2cos2a

Answer 1

$-cos^2 alpha +2cos2 alpha =-cos^2 alpha +2(cos^2 alpha -sin^2 alpha )=$$-cos^2 alpha+2cos^2 alpha -2sin^2 alpha =cos^2 alpha -2sin^2 alpha$$=1-sin^2 alpha -2sin^2 alpha =1-3sin^2 alpha$