Question

integral of cos5x cos3x dx

Answer 1

Use the identity \(\cos x\cos y= \frac{1}{2}[\cos(x-y)+\cos(x+y)]\), we have
\[\cos5x \cos3x = \frac{1}{2}[\cos(5x-3x)+\cos(5x+3x)]\]
Then, integrate it. It shouldn't be difficult.

Answer 2

Welcome to OpenStudy!
Often trig identities can be used to simplify integration. In RolyPoly's second equation, combine: 5x-3x and 5x+3x. Re-write that second equation in simplified form and then ask yourself how you'd integrate the two resulting terms.