Copy of 3 planes (One common LINE of intersection)
1. Right-click on one of the planes, and while pressing down on your mouse (or trackpad), rotate the planes to see how the figure looks like from different angles by moving your mouse (or finger on your trackpad). 2. Let go of your cursor, and deselect the green OR red plane by clicking on the corresponding circles in the left menu. Notice now that the two planes are hidden, and observe the intersection between the green and red planes.
In this case, what is the intersection between the green and red planes ? Hence, what conclusion can you draw from how we can determine the number of common points of intersection between any 2 planes, by investigating the intersection between the green and red plane.