1. ## Evaluate the Integral

I ended up with 9/8xsin(8x)-9/8sin(8x) and am not sure what am i missing.

On a side note, how can I input that problem into Wolfram Mathematica? I tried Integrate[9xCos(8x) dx, x] and it gave me a strange value.

2. Originally Posted by masterofcheese

I ended up with 9/8xsin(8x)-9/8sin(8x) and am not sure what am i missing.

On a side note, how can I input that problem into Wolfram Mathematica? I tried Integrate[9xCos(8x) dx, x] and it gave me a strange value.
What method did you use?

P.S. Try "integrate 9*x*cos(8*x)"

3. Oh, sorry, forgot to say, but this is integration by parts.