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Math Help - integral of xsinx^2

  1. #1
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    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 =/
    help please
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  2. #2
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    Quote Originally Posted by xslim12 View Post
    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 =/
    help please
    What have you set to u and what to dv ?

    ZB
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  3. #3
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    i set u=x du=1 dv=sin(x^2) v=(1/2x)sin(x^2)
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  4. #4
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    Quote Originally Posted by xslim12 View Post
    i set u=x du=1 dv=sin(x^2) v=(1/2x)sin(x^2)
    If dv=sin(x^2), v does not equal (1/2x)sin(x^2), as you have to integrate dv to get 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
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  5. #5
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    Quote Originally Posted by xslim12 View Post
    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 =/
    help please
    Set u=x^2
    du=2xdx

    From there, you just integrate 0.5sin(u)
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  6. #6
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    Quote Originally Posted by colby2152 View Post
    Set u=x^2
    du=2xdx

    From there, you just integrate 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
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  7. #7
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    Quote Originally Posted by xslim12 View Post
    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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