Question

integral of sin (3x) cos^6 (3x)

Answer 1

Let u = cos(3x)

Answer 2

\[
\int \sin(3x)\cos^{6}(3x)dx \\
\text{Let } u = \cos(3x) \\
du = -3\sin(3x)dx \\
\sin(3x)dx = -\frac 13du \\
\int \sin(3x)\cos^{6}(3x)dx = \int -\frac 13 u^6du = -\frac 13 \frac{u^7}{7} = \\
-\frac{1}{21}\cos^7(3x) + C\\
\]

Answer 3

Thanks :)

Answer 4

you are welcome.