First question: I need to graph (in R^2 ) equations like
x + y = 0 and x - y = 0
I cannot use directly the option Plot. How can I do it?
Second question: I need to graph in R^3 the "lines" like
x + y + z ==10
x + y == 5
x + z == 5
y + y == 5
say, in the neighborhood of the origin <= 20 (to visualize the "positive part").. May I use the packet Graphics3D? How?
In this case I am completely lost and a bit desesperated!.