Given:
$\displaylines{ f(x,y) = &5xy, 0<x, y<1 \\ &0, elsewhere}$
find the expected value of: $z=\sqrt{x^2+y^2}$
do I solve using the integral:
$\int_{0}^{1}\int_{0}^{1}f(x,y)z dxdy$
or do i use: $\int_{0}^{\infty}\int_{-\infty}^{1}f(x,y)zdxdy$
Please explain how you select the bounds of the integral.