Question

Jika A+B = TT/3 dan cos A cos B = 5/8, maka cos (A-B) =

Answer 1

A+B = 60
cos (A+B) = cosA.cosB - sinA.sinB
cos60 = 5/8 - sinA.sinB
1/2 = 5/8 - sinA.sinB
sinA.sinB = 5/8 - 1/2 = 1/8

cos(A-B) = cosA.cosB + sinA.sinB
cos(A-B) = 5/8 + 1/8
cos(A-B) = 6/8 = 3/4