It is given that
∫ cos 4x cos 3x dx
Using the formula cos x × cos y = 1/2(cos(x + y) + cos(x - y))
∫ cos 4x cos 3x dx = 1/2 ∫(cos 7x + cos x) dx
On further simplification
∫ cos 4x cos 3x dx = 1/2 ∫ cos 7x dx + 1/2 ∫ cos x dx
By integrating w.r.t. x
∫ cos 4x cos 3x dx =
