Jika A + B = π/3 dan cod A cos B = 5/8, maka cos (A-B) adalah...

jawab
trigonometri

cos (A + B) =  cos A  cos B - sin A sin B
cos π/3 = 5/8 - sin A sin B
1/2 = 5/8 - sin A sin B
sin A sin B =  5/8 - 1/2 = 1/8

cos (A - B) = cos A cos B + sin A sin B
= 5/8 + 1/8
= 6/8
= 3/4