It can either have zero or one I think but I'm honestly not sure. I'm trying to figure it out my self right now.
None, one or an infinite number.In graph form, the three correspond to:None = Parallel linesOne = Interscting linesInfinite = Coincident lines.
Either an infinite number or none.
An example is x+y=3 and 2y+x=5 these are more or less known as simultaenous equations
Let the number of unknowns be N. The solution space may have N, N-1, ..., 0 dimensions or may not exist. If a solution exists and the dimension of the solution space is 0, then there is exactly one...