Evaluate $\displaystyle \iint\limits_R \frac{1}{(1 + x^2 + y^2)^\frac{3}{2}} dx dy$

where $\displaystyle R $ is the region bounded by the straight lines $\displaystyle y=0 , x=1 , y=x $

if i use polar transformation, what will be the ranges of integration? or is there any way other than polar transformation?