Question

Jika A+B =2π/3 dan cos A dikali cos B=3/9. nilai cos (A-B) adalah

Answer 1

A + B = 2π/3 = 120°
π = 180°

cos (A + B) = cos 120° = -1/2
cos A cos B - sin A sin B = -1/2
3/9 - sin A sin B = -1/2
sin A sin B = 1/3 + 1/2 = 5/6

cos (A - B)
= cos a cos b + sin a sin b
= 3/9 + 5/6
= 1/3 + 5/6
= (2 + 5)/6
= 7/6