Question

sa se calculeze mumarul sin 60°•cos 150°

Answer 1

cos 150° = cos(90°+60°)= cos90°cos60°-sin90°sin60°=> cos(90°+60°) = 0*1/2-1*√3/2=>
cos(90°+60°)= -√3/2

sin60*cos150= √3/2*(-√3/2)= -√9/4 = -3/4

Answer 2

$\displaystyle sin60\cdot cos150=\frac{\sqrt3}{2}\cdot [-cos(180-150)]=\frac{\sqrt3}{2}\cdot \Big(-\frac{\sqrt3}{2}\Big)=-\frac{3}{4}$