Question

Calculus - > Integral -> Substitution
The question is sin 3x cos 3x dx

Solve it by integrating using substitution.

Answer 1

Do you know what the derivate of \[\Large \sin(3x)  \] is?

Answer 2

derivative*

Answer 3

HINT: Let u be sin(3x).

Answer 4

How do you choose what to let u be? In this case you choose sin(3x) but why?

Answer 5

Takes some practice, but in case you consider taking u=cos(3x), that would also work. It's mainly about developing the idea of substitution. If you choose u=sin(3x) then:

\[\Large \frac{du}{dx}=3\cos(3x) \]