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Math Help - need calc help

  1. #1
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    need calc help

    solve the integral of (r)(e^(r/2))dr


    i got (2re^(r/2) - e^(r/2))/4 + C
    ..but that's not right.

    Can you please explain or show me the correct procedure.
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  2. #2
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    Quote Originally Posted by twilightstr View Post
    solve the integral of (r)(e^(r/2))dr
    i got (2re^(r/2) - e^(r/2))/4 + C
    ..but that's not right.
    What makes you think that is not correct?
    Differentiate that answer to see if it is correct.
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  3. #3
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    Quote Originally Posted by twilightstr View Post
    solve the integral of (r)(e^(r/2))dr


    i got (2re^(r/2) - e^(r/2))/4 + C
    ..but that's not right.

    Can you please explain or show me the correct procedure.
    Looking at your answer makes me think you did a small silly mistake in the second integral of integration by parts.

    \int r e^{\frac{r}2} \, dr  =  r \dfrac{e^{\frac{r}2}}{\frac12} - \int \dfrac{e^{\frac{r}2}}{\frac12}\, dr  = 2r e^{\frac{r}2} - \int 2e^{\frac{r}2} \, dr = 2r e^{\frac{r}2} - 2\dfrac{e^{\frac{r}2}}{\frac12} = 2r e^{\frac{r}2} - 4e^{\frac{r}2}
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