hi just confused on this integration.
$\displaystyle
\int xcosx
$
how would i go about solving?
There are many techniques. One such is integration by parts. You'll find it done as an example somewhere in here: http://en.wikipedia.org/wiki/Integra...#More_examples.
$\displaystyle \frac{dy}{dx} = \sin x + x \cos x$
Integrate both sides with respect to x:
$\displaystyle y = \int \sin x + x \cos x \, dx = \int \sin x \, dx + \int x \cos x \, dx = - \cos x + \int x \cos x \, dx$
Substitute $\displaystyle y = x \sin x$:
$\displaystyle x \sin x = - \cos x + \int x \cos x \, dx$
Now re-arrange to make $\displaystyle \int x \cos x \, dx$ the subject and add a "+ C".
Next time post the whole question - as you can now see the first part was essential to answering the second part.