Hi Onur,
Yes, those are each an equation for a line in 2-D space.
If you mean for equation 1 to define a line in the X-Z plane, then you must also require y=0.
If you mean equation 2 to define a line in the Y-Z plane then x=0 is required.
In 3-space, two lines may or may not lie in the same plane. In linear algebra, they lie in the same plane iff there is an R3->R2 projection operator which leaves both lines unchanged.
Best,
David
