Question

sinx-cosx=3/корень из 10
найти cos4x

Answer 1

(sin x-cos x)^2 = 9/10
sin^2 x - 2sin x*cos x + cos^2 x = 9/10
1 - sin 2x = 9/10
sin 2x = 1/10
Cos 4x = 1 - 2sin^2 (2x) = 1 - 2/100 = 98/100 = 0,98