I have a double integral of $1dxdy$, where the area is given by $x=[-1,3]$ and $y=[-4,1]$
I can just evaluate the integral by inspection, but I was wondering how to calculate this more properly. I tried rewriting in polar coordinates, but I got stuck since the lengths of the sides don't give useful values of theta.
Does anyone know if it is possible to evaluate this integral by other means then inspection?
Thanks in advance!