Cos ( x - 3π/2) = -4/5 угол х в 1-ой четверти
cos ( x - 3π/2) = - sin ( x ) = -4/5 sin x = 4/5 cos x = √(1 - 16/25) = 3/5
sin 2x = 2·sinx·cosx = 2·3/5 ·4/5 = 24/25
cos2x = √1 - (24/25)² = √49/625 = 7/25
sin 0.5x · cos 2.5x = 0.5(sin 3x + sin (-x)) = 0.5(sin(2x + x) - sinx) =
= 0.5(sin2x·cosx + sinx · cos2x - sinx) = 0.5(24/25 · 3/5 + 4/5 · 7/25 - 4/5) =
= 0.5·(72/125 + 28/125 - 4/5) = 0.5 (100/125 -4/5) = 0,5 (4/5 -4/5) = 0