I am studying for an analytic geometry, final but I am totally lost for this problem... We didn't even cover this topic in class (my prof didn't show up for class for two weeks) and I have no clue on how to do it. If anyone could help I would appreciate it.
Question: Prove that the equation $x^2-y^2+xy-1=0$ is a ruled surface.
I understand that a ruled surface is a surface composed of straight lines but that is as far as my knowledge goes for this question... Again any help is appreciated.
In this case: no $z\implies$ is an (hyperbolic) cylinder $\implies$ obviously a ruled surface.