Let $Dsub{R}^2$ be the region in the upper half plane bounded by $x^2+y^2=4,y=x$ and $y=-x.$

a$)$ Set up an iterated integral for the area of $D$ in any coordinate system of your choice.

b$)$ Calculate the area of $D$ using the iterated integral in part $($a$).$

c$)$ Evaluate the integral ${}_{D}f(x,y)dA,$ where $f(x,y)=\frac{1}{(x^2+y^2{)}^{\frac{3}{2}}},$ in polar coordinates.