segitiga abc lancip, cosA=4/5 dan sinB=12/13 maka cos(A-B)= beserta caranya

Jawab :

cos A = 4/5
tripel Pythagoras : 3,4,5
sin A = 3/5

sin B = 12/13
tripel Pythagoras : 5,12,13
cos B = 5/13

cos (A - B)
= cos A cos B + sin A sin B
= 4/5 . 5/13 + 3/5 . 12/3
= (20 + 36)/65
= 56/65