1. Of what type is Poisson’s equation uxx + uyy = f(x,y) ? I used that if you have auxx+buxy+cuyy+dux+euy +fu+g=0 where a, b, c, d, e, f, g is constants, and if b^2-4ac<0 then you get an elliptic type because b=0, a=1, c=1 gives 0^2-4*1*1=-4<0 => elliptic Is this right? And why do i have to do like this? i don't understand the meaning of type.