Jawabanmu

2013-12-10T11:51:31+07:00
Cos A . Cos B = 

1/2 { cos(A+B) + cos(A-B) }
2013-12-10T12:24:08+07:00
Cos A . Cos B = 

1/2 < cos(A+B) + cos(A-B) >