My subject about the canonical form of PDE. I had many exercises to do and they were fine, but I'm stuck with this one: $$U_{xx}-yU_{xy}+xU_x+yU_y+u=0$$ So first we have to calculate $B-4AC=y^2-4$. I couldn't determine what ether hyperbolic or elliptic or parabolic?
Could you help me to get the canonical form? Thanks in advance.