Equation of a plane and the dot product
A plane in space is uniquely determined by knowing a point  on the plane and a vector  that is perpendicular, or normal, to the plane.
The plane consists of all points  such that the vector from  to , namely , is perpendicular to the normal vector . In other words, the plane is the set of all points  such that .
Drag points  and  as well as the tip of the normal vector  and observe how the equation changes.
Developed for use with Thomas' Calculus, published by Pearson.