It is known that ABCD and abef are two squares and not in the same plane, m and N are the points on the diagonal AC and FB respectively, and am = FN It is suggested that the extension line connecting an and be should be connected to g

It is known that ABCD and abef are two squares and not in the same plane, m and N are the points on the diagonal AC and FB respectively, and am = FN It is suggested that the extension line connecting an and be should be connected to g

Connect AE
Because it's Square and am = FN
So am / AC = an / AF
It is concluded that Mn is parallel to FC
FC belongs to planar CBE
Mn ‖ plane CBE