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# C4: Integration by parts watch

1. INTEGRAL: x cosx dx = x sinx + cosx + c

Erm.......
2. err i got cosx+xsinx +c but i did it quickly....

and how come this is in your C4? surely its C3
3. (Original post by FoOtYdUdE)
INTEGRAL: x cosx dx = x sinx + cosx + c

Erm.......
x=u and cosx=dv/dx therfore v=sinx and du/dx=1
uv-f(v*du/dx) where f=intergral of...
=>xsinx+cosx + c
4. You're right:
http://www.wolframalpha.com/input/?i=integrate+xcosx
5. (Original post by zevy1)
x=u and cosx=dv/dx therfore v=sinx and du/dx=1
uv-f(v*du/dx) where f=intergral of...
=>xsinx-cosx + c
Integrating sinx gets -cosx
the negative signs cancel
6. (Original post by doivid)
Integrating sinx gets -cosx
the negative signs cancel
Sorry typo, i changed it now

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