Answer
$x^2+y^2 \leq 9$ and this is the region inside the circle $x^2+y^2=9$
Work Step by Step
Consider $\iint_{R} f(x,y) dA=\iint_{R} (x^2+y^2-9) dA$
The integral will be a minimum on the region when $x^2+y^2-9 \leq 0$
This implies that $x^2+y^2 \leq 9$ and this is the region inside the circle $x^2+y^2=9$
