Question

Resolver las siguientes integrales
∫sen(5x) cos(4x)dx

Answer 1

Identidad trigonométrica:

sen(a) . cos(b) = 1/2 [sen(a + b) + sen(a - b)]

a = 5 x; b = 4 x; a + b = 9 x; a - b = x

Queda: 1/2 ∫[sen(9 x) + sen(x)] dx =

= - 1/2 [1/9 cos(9 x) + cos(x)

= - 1/18 cos(9 x) + 1/2 cos(x)

Mateo