Originally Posted by

**HallsofIvy** Am I understanding this correctly? You have found that the equation of the plane is Ax+ By+ Cz= D and you want to "define this plane by three points instead." In other words, you just want to find three points that lie on that plane. It you take x= y= 0 then z= D/C so (0, 0, D/C) is a point on the plane. If x= z= 0, then By= D so y= D/B. (0, D/B, 0) is a point on that plane. I'll leave the third point to you.

I think TKHunny was misunderstanding the problem, thinking that A, B, and C were three points that you wished to use to find the equation of the plane.