How do I evaluate the integral [integral] x^2 cos mx dx using u-substitution?

[Zack88]

I have to evaluate the integral

problem: [integral] x^2 cos mx dx

my solution w/ steps: u = x^2, du = 2x. dv = cos mx, v = sin mx / m

(x^2)(sin mx / m) - [integral] (sin mx / m)(2x)

(x^2)(sin mx / m) - 2 [integral] (sin mx / m) (x)

(x^2)(sin mx / m) + 2 (cos mx / m) + c [is this correct?]

any help would be appreciated.

 

[rock.freak667]

you need to integrate (xsinmx)/m by parts again.

 

[Zack88]

ok when should I do that after which step?

 

[Zack88]

wait what would that look like?

(xsinmx)/m

u = ? dv = ?

 

[rock.freak667]

try u=x and dv=sinmx/m dx