sine and cosine

Question

angles A and B are located in the first quadrant. if sinA=5/13 and cosB=3/5, determine the exact value of cos(A+B)

Answer 1

sinA=5/13 means adj side is 12

cosB=3/5 means opp side is 4

cos(A+B)=cosAcosB-sinAsinB

cos(A+B)=(12/13)(3/5)-(5/13)((4/5)

cos(A+B)=(36/65)-(20/65)

cos(A+B)=16/65