Coincident Planes
Two planes are coincident when they have the same or parallel normal vectors and their equations are scalar multiples of each other. In this example, the two planes are x + 2y + 3z = -4 and 2x + 4y + 6z = -8. Notice from the example how they have the same normal vector, and how the coefficients of the second equation are all double the coefficients of the first equation.
How many points of intersection are there between these two planes?