Reflecting about z = y
Move A, B, and C around so that the plane DOES NOT DISAPPEAR and so that each of these points has both z and y coordinates equal to each other. (This will cause the plane to have equation z = y).
Drag O (preimage) to different positions. Record the coordinates of O in the PREIMAGE column. Record coordinates of its reflection in the plane in the IMAGE column.
What do you notice? Describe.
Suppose point O = (a, b, c). What would its image O' be if O was reflected about the plane z = y?