Question

Evaluate : ∫sin3x.cos4x dx

Answer 1

Let I = ∫ sin 3x.cos 4x dx

USE:

sin A. cos B = 1/2[sin(A + B) + sin(A + B)]

= 1/2∫ [sin(3x + 4x) + sin(3x – 4x)] dx

= 1/2∫ [sin7x + sin(-x)] dx

= 1/2∫[sin7x + sin x] dx