# Math Help - need calc help

1. ## 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.

2. Originally Posted by twilightstr
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.

3. Originally Posted by twilightstr
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.

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