y = 1-cosx

cosx: [-1; 1],  E(y): [0; 2]

y = 1 - 4cos2x

cos2x: [-1; 1],  E(y): [-3; 5]

Эх.. надеюсь то)) 

y = (1/2) sinx*cosx - 1 = (sin2x)/4  -1

sin2x: [-1; 1],   E(y): [(-5/4); (-3/4)]