∫〖Sin^(2 ) x cos2x dx〗 ( solving it, getting + c) could need some help

[Gillyjay]

Homework Statement

∫〖Sin^(2 ) x * cos2x dx〗

Homework Equations

The right answer should be: sin 2x / 4 - x/4 - sin4x / 16

The Attempt at a Solution

If i would set Sin^(2 ) x= (1-cos2x)/2 I can replace it in the integral
Then we get:
∫▒〖(1-cos2x)/2 cos2x dx〗
As far as I am concerned we cannot use the constant multiple rule because there is no constant to multiply

I don’t know how to go on from here to solve it 

 

[vela]

OK, so you have

\begin{align*}<br /> \int \sin^2 x\cos 2x\,dx &amp;= \int\left(\frac{1-\cos 2x}{2}\right)\cos 2x\,dx \\ <br /> &amp;= \frac{1}{2}\int(\cos 2x - \cos^2 2x)\,dx \\<br /> &amp;= \frac{1}{2}\int\cos 2x\,dx - \frac{1}{2}\int \cos^2 2x\,dx<br /> \end{align*}

Can you take it from there?

Hint: use a trig identity for cos² 2x.