# Thread: Problems with an Integral

1. ## Problems with an Integral

$\displaystyle \int x^2 cos(mx) dx$

I have trouble solving this. I know that i have to integrate by parts, but somehow i always get the wrong answer.... I put it into Wolframalpha, but im having a hard time following its solution

any help would be appreciated

2. Originally Posted by coobe
$\displaystyle \int x^2 cos(mx) dx$

I have trouble solving this. I know that i have to integrate by parts, but somehow i always get the wrong answer.... I put it into Wolframalpha, but im having a hard time following its solution

any help would be appreciated
tabular integration ...

Code:
.............. u ........... dv

+ .............x^2 ........ cos(mx)

- ............ 2x ..........(1/m)sin(mx)

+ ............. 2 ......... -(1/m^2)cos(mx)

- ............. 0 ...........-(1/m^3)sin(mx) 
$\displaystyle \textcolor{red}{\frac{x^2}{m} \sin(mx)} + \textcolor{green}{\frac{2x}{m^2}\cos(mx)} \textcolor{blue}{- \frac{2}{m^3}\sin(mx)} + C$