Yg tau mohon bantuannya..

cos (A+B) = cos (π/3) = cos (60°) = 1/2 = cosAcosB - sinAsinB
1/2 = 5/8 - sinAsinB
sinAsinB = 1/8
cos (A-B) = cosAcosB + sinAsinB
= 5/8 + 1/8
= 6/8 = 3/4