How can we calculate the sinus of 120°?

We can observe that120° represents the sum of two common angles: 30° and 90°. So we can rewrite sin(120°) as sin(30°+90°). Now we are going to use this trigonometric formula in order to calculate the sinuns: sin(A+B)=sin A cos B + cos A sin B. In our situation: sin(30°+90°)= sin30° x cos90° + cos30° x sin90°, where sin30° = 1/2, cos30°=sqrt(3)/2 and sin90°= 1, cos 90°= 0=> sin(30°+90°) = 1/2 x 0 + sqrt(3)/2 x 1= 0 +  sqrt(3)/2= sqrt(3)/2.