The given domain is $\displaystyle D=D_1\cup D_2$ where: $\displaystyle D_1\equiv \left \{ \begin{matrix}0\leq y\leq 1\\0\leq x\leq\sqrt{y}\end{matrix}\right. \;,\quad D_2\equiv \left \{ \begin{matrix}1\leq y\leq 2\\0\leq x\leq 2-y\end{matrix}\right.$