1. ## integral of xsinx^2

Integral of xsin(x^2)
ok, so the answer is .-.5cox^2
however, when i do integration by parts i get -.5cos(x^2)+(1/2x)Cos(x^2)
i cant seem to figure out what i am doing wrong =/

2. Originally Posted by xslim12
Integral of xsin(x^2)
ok, so the answer is .-.5cox^2
however, when i do integration by parts i get -.5cos(x^2)+(1/2x)Cos(x^2)
i cant seem to figure out what i am doing wrong =/
What have you set to $\displaystyle u$ and what to $\displaystyle dv$ ?

ZB

3. i set u=x du=1 dv=sin(x^2) v=(1/2x)sin(x^2)

4. Originally Posted by xslim12
i set u=x du=1 dv=sin(x^2) v=(1/2x)sin(x^2)
If $\displaystyle dv=sin(x^2)$, $\displaystyle v$ does not equal $\displaystyle (1/2x)sin(x^2)$, as you have to integrate $\displaystyle dv$ to get $\displaystyle v$.

Also (1/2x)sin(x^2) is ambiguous, it could mean (1/(2x))sin(x^2) or =((1/2)x)sin(x^2)

ZB

5. Originally Posted by xslim12
Integral of xsin(x^2)
ok, so the answer is .-.5cox^2
however, when i do integration by parts i get -.5cos(x^2)+(1/2x)Cos(x^2)
i cant seem to figure out what i am doing wrong =/
Set $\displaystyle u=x^2$
$\displaystyle du=2xdx$

From there, you just integrate $\displaystyle 0.5sin(u)$

6. Originally Posted by colby2152
Set $\displaystyle u=x^2$
$\displaystyle du=2xdx$

From there, you just integrate $\displaystyle 0.5sin(u)$
Thanks, i also tried substitution, but forgot to take the extra x out.
Thanks again man! I really got to stop making dumb mistakes

7. Originally Posted by xslim12
Thanks, i also tried substitution, but forgot to take the extra x out.
Thanks again man! I really got to stop making dumb mistakes
Trust me, you'll eliminate a lot of dumb mistakes (but never all!). Practice makes perfect, so keep up the good work.

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# xsinx2 integration

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