Vectors 8.5 The Cartesian Equation of a Plane
Channel: Ms Havrot's Canadian University Math Prerequisites
Date: 06/03/2020

Ax + By + Cz + D = 0  where  vector (A, B, C,) is the normal to the plane.
If you don't have the normal you will need to take the cross product of the two direction vectors in your plane first.  We also find the angle between two planes by finding the angle between their normals.