# Thread: Combining the sum of the double integrals

1. ## Combining the sum of the double integrals

Hey Guys,

I need help with combining this integral into one single integral. (No need to evaluate.)

$
\int_{0}^{2} \int_{0}^{x} \sqrt {x^2 + y^2} dydx + \int_{0}^{2\sqrt 2} \int_{0}^{\sqrt {8-x^2}} \sqrt {x^2 + y^2}
dydx
$

I have drawn the images of my boundaries, but I have no clue where to go from there. I was thinking of using symmetry at first, but I don't know how to set it up properly.

Thanks for any help,
TJ

2. Hello,

What about substituting into polar coordinates ?

3. Oh, I must have accidentally erased that part...

I did try in polar, but the r doesn't work.
Or at least I'm not sure how to set it up for left integral and then adding them all up together.