The Intersection of Moving Planes

The system of equations

			 x+2y+m z==-1

			 2x +y-z==3

			 m x-2y+ z== 1

represents three planes in space. As m changes in value the first and last planes move in space, and the solution to the moving system is illustrated by the animation sequence  below. Initially the three planes meet in a point but as the value of m changes the position of the solution changes, and for 2 specific values of m, (-5 and 1)  the nature of the solution changes. Click in the right cell bracket below, and start the animation by pressing Ctrl Y