[math]\text{Double integral in polar coordinate system}\\\\ \iint_D(x^2+y^2)dxdy,\,\,\,D:\,x^2+y^2\leq1\leq x+y\\\\\text{I need to find range of r so:}\\\\(1)\,\,x^2+y^2\leq1 \Rightarrow\,\,r^2\leq1\,\,\Rightarrow\,\,r\in[0,1]\\\\(2)\,\,x+y\geq1\,\,\Rightarrow r\cos\varphi+r\sin\varphi\geq1\,\,\Rightarrow r(\sin\varphi+\cos\varphi)\geq1\\\\\text{I'm confused how to solve it for r?}[/math]