[Math] Prove that if through three given points two planes can be drawn, then infinitely many planes throught these points can be drawn.

3dgeometry

Prove that if through three given points two planes can be drawn, then infinitely many planes through these points can be drawn. I don't get how this is possible, since there is unique plane passing through three point, how would I get two planes?

Best Answer

Beware the hidden assumption."There is a unique plane passing through 3 points." This is only true if the 3 points are not co-linear. Don't assume the points are NOT co-linear. If 2 planes intersect, their intersection is a line, and there are infinitely planes containing that line. So if 3 points are co-linear, there are infinitely many planes through the line that contains the 3 points.