Im trying to check my answers to a problem, and in the past i've used a 3d grapher to graph functions like f(x,y) = whatever. but now i need to find a tangent plane to a surface at a point. the surface is: x2y+y2z-z2x=1 but i dont know how to go about graphing something expressed that way. are there different names to these types of graphs? are there programs that will graph things expressed other than z=[stuff w/ x and y]?