# Homework Help: Double integral tough

1. Jun 5, 2010

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

$\int_{0}^{1} \int_{0}^{1} \sqrt{4x^2 + 4y^2 + 1} dx\,dy$

3. The attempt at a solution

This integral is tough for me, I couldn't think of a way to evaluate it. Can you suggest me the first step to do this problem?

Thanks!

2. Jun 5, 2010

### CompuChip

The sum of squares strongly suggests a change to spherical coordinates (in 2D, that would be polar coordinates).

An integral like
$$\int r \sqrt{1 + r^2} \, dr$$
is easier, because r is the derivative of 1 + r2.