# Math Help - integration

1. ## integration

$dv=cos5xdx ==> v= \frac 1{5} sin5x$

can someone show me how to get that?

2. Originally Posted by jeph
$dv=cos5xdx ==> v= \frac 1{5} sin5x$

can someone show me how to get that?
First you should notice that what you have is:

$\frac{dv}{dx}= \cos(5\,x)$

Now the function whose derivative is $\cos$ is $\sin$, so we try $w(x)=\sin(5\,x)$ differentiating we find the derivative is $5\,\cos(5\,x)$, so we need:

$v=\frac{1}{5} \sin(5\,x)$

RonL