Morphing one square to another :[br]Let P and Q moving proportionally on D'B and B'D.[br]When P goes from D' to B, the square C'D'AB' becomes ABCD. [br]As there is a common vertex, the points O and O' describe the diagonal C'A and AC.[br]When P is at the middle of D'B, Q is at the middle of B'D, O at the middle of C'A and O is at the middle of AC.[br]Moins