Primeiro é necessário saber o cos (x) e sen (y).
Para tanto, devemos saber:
sen^2 (a) + cos^2 (a) = 1
(3/5)^2+cos^2 (x) = 1
cos^2 (x) = 1-(9/25)
cos^2 (x) = 16/25
cos (x) = 4/5
sen^2 (y) + (5/13)^2 = 1
sen^2 (y) = 144/169
sen (y) = 12/13
A)
sen(x+y)
sen(x).cos(y)+sen(y).cos(x)
(3/5).(5/13)+(12/13).(4/5)
15/65+48/65
63/65
B)
cos(x+y)
cos(x).cos(y)-sen(x).sen(y)
(4/5).(5/13)-(3/5).(12/13)
20/65-36/65
-16/65
