Вычислите, используя формулы : cos150, sin135, cctg240, cos210

Cos150°=cos(90°+60°)=cos(π/2 +60°)= - sin60°= - √3/2
sin135°=sin(90°+45°)=sin(π/2+45°)= cos45°=√2/2
ctg240°=ctg(180°+60°)=ctg(π+60°)=ctg60°= 1/√3
cos210°=cos(180°+30°) = cos(π+30°) = - cos30° = - √3/2