# Double Integral

tnutty

## Homework Statement

$$\int_{D}\int y^2$$
where D = {(x,y) | -1 $$\leq$$ y $$\leq1$$, -y-2$$\leq x\leq y$$

The integral I set up is below :

$$\int^{1}_{-1} \int^{y}_{-y-2} y^2 dx dy$$

From that I get the answer 0, but the book says its 4/3.

I get 0 because It reduces to this integral :

$$\int^{-1}_{1} 2y^3 + 2y$$

Any idea where I could be wrong?

anubis01

## Homework Statement

$$\int_{D}\int y^2$$
where D = {(x,y) | -1 $$\leq$$ y $$\leq1$$, -y-2$$\leq x\leq y$$

The integral I set up is below :

$$\int^{1}_{-1} \int^{y}_{-y-2} y^2 dx dy$$

From that I get the answer 0, but the book says its 4/3.

I get 0 because It reduces to this integral :

$$\int^{-1}_{1} 2y^3 + 2y$$

Any idea where I could be wrong?

In your last step you reversed your bounds, it should be (-1,1) not (1,-1) as you wrote. Also the final step should be $$\int$$2y3 +2y2 dy with the bounds (-1 to 1).

Last edited:
Homework Helper
Hi tnutty!
Any idea where I could be wrong?

erm

2y3 + 2y2 ?

tnutty
I mean to write 2y^3 + 2y^2. But its was the bounds. Thanks guys.