properties of parellelogram

We can clearly see the figure. This is a parallelogram ABCD. We can change the positions of the three points A, B, and C. We cannot move the position of the point D because D will move automatically to keep ABCD a parallelogram. Shape and size of the parallelogram depends upon the position of these four points. AD and BC are the two diagonals of this parallelogram and they intersect at E. Let us move the free objects A, B and C and observe how the shape of the parallelogram, angles, lengths of sides and lengths of diagonals get changed