Question

Diketahui segitiga ABC, cos A =3/7, dan Sin B = 2/3, maka nilai cosc =

Answer 1

Cos A = 3/7
sin A = 2akar10 / 7

sin B = 2/3
cos B = akar5 / 3

cos C = cos (A+B)
maka ;
cos A cos B - sin A sin B
= 3/7 × akar5/3 - 2akar10 / 7 × 2/3
= 1/7 akar5 - 4akar10 / 21
= 3akar5 - 4akar10 / 21