# Real analysis – How to proceed with this integral?

Leave $$G: = {(x, y) in mathbb {R} ^ 2: 0 1 }$$
I want

calculate this integral:
$$int_G x ^ 2$$

I want to try polar coordinators:
so established

$$(x; y) = (rcos ( phi); rsin ( phi))$$

I'm not sure how to get the right limits for $$phi$$
It is not
$$x ^ 2 + y ^ 2 = r ^ 2$$ ?

Any help much appreciated!