Homework Help: Double integration problem

1. Mar 28, 2009

Enzo

1. The problem statement, all variables and given/known data

$$\int^1_y\int^1_0 x^2*e^{xy} dydx$$

Answer: $$1/2 (e-2)$$

3. The attempt at a solution

I've tried about 4 ways of doing this, I can't solve it. It either ends up being a completely huge and wrong answer, or ends up giving me a integration by parts of something like $$\int e^(x^2) dx$$ which I cant solve

Last edited: Mar 28, 2009
2. Mar 29, 2009

tiny-tim

Hi Enzo!

(have an integral: ∫ and try using the X2 tag just above the Reply box )
Did you change the order of integration first?

I get ∫xex2 dx, which is easy

Try again!

3. Mar 29, 2009

HallsofIvy

This makes no sense. The way you have it written, with the "outer integral" from y to 1, the answer must be a function of y, not a constant. But, as written it does not give "$e^{x^2}$
$$\int_{x=y}^1\int_{y= 0}^1 x^2e^{xy}dy dx= \int_{x=y}^1\left(xe^{xy}\right)_0^1 dx$$
$$= \int_{x=y}^1 \left(xe^x- x\right)dx$$
which can be done by a single integration by parts.

If it were
[tex]\int_{y=0}^1\int{x=y}^1 x^2e^{xy}dx dy[/itex]
tat can be done by two integrations by parts.

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