# Integration by parts problem.

1. Sep 8, 2009

### CandyApples

1. The problem statement, all variables and given/known data
Let F(b) be the exact area under the graph of y = x2*e-x between x=0 and x=b for b>0. Find the formula for F(b).

2. Relevant equations
int(uv')= uv - int(vdu)

3. The attempt at a solution
u = x2 and dv = e-x, thus u'=2xdx and v=-e-x.

y= -x2*e-x - -2*integral(xe-x).
= -x2*e-x -2xe-x-2e-x.

This does not yield the correct equation, so where did i make a mistake?

2. Sep 8, 2009

### LeonhardEuler

Did you remember that this is a definite integral from 0 to b?

3. Sep 8, 2009

### CandyApples

yes, and this resulted in the previous answer with b's subbed in for the x's then +2 since the only term left would be - -2 when zero is plugged in.

4. Sep 8, 2009

### LeonhardEuler

Then I don't see what's wrong with your answer. Why do you think it's wrong?

5. Sep 8, 2009

### CandyApples

it is a webassign problem, so it gives me a red x when I am wrong. I probably just need to fix notation somewhere, thank you for verifying that the integral is correct though :).

6. Sep 8, 2009

### CandyApples

Issue resolved, i accidentally had a double - that i had to check over a couple times to notice. Man I hate webassign lol.

7. Sep 8, 2009

### Jay J

haha SBU im assuming?

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