What actually is an invariant line? The points on the line move
An invariant line is one for which, under a given transformation, all points on the line are their own image. I'm not sure what you mean by them moving?
An invariant line is one for which, under a given transformation, all points on the line are their own image. I'm not sure what you mean by them moving?
Fair. My description would be "a line of invariant points", right? I get confused. Don't even do this FP4 stuff.
If a point is its own image, for all points, then you have the identity transformation. But an invariant line is one where a point on a line maps to a possibly different point on the line, as with a shear.