Where Did I Go Wrong in My Integration by Parts Problem?

[CandyApples]

Homework Statement

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).

Homework Equations

int(uv')= uv - int(vdu)

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?

 

[LeonhardEuler]

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

 

[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.

 

[LeonhardEuler]

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

 

[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 :).

 

[CandyApples]

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

 

[Jay J]

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

haha SBU I am assuming?

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