a) (cos120°-tg150°)²= (cos(180°-60°)-tg(180°-30°))²= (-cos60°-tg30°)²= -1/2 -√3/3)²=1/4+3/9=9/36+12/36=21/36
b) 2cos120°+4tg150°xsin 120°= -2cos60°-4tg30°+xsin60°=-2* 1/2 - 4* √3/3 + x*√3/2 = -1 -4√3/3 + x√3/2
c) sin 135°+cos150°+tg120°= sin45°+cos30°+tg60°= √2/2 + √3/2 + √3