Shapes
When two pairs of parallel lines intersecting each others as left diagram.
If length of lines ab, bc, cd & ad are equal as well as the angles of intersection are right angles.
The four line form a square.
If line bc shift to the right and we have length of line ab equal line dc and length of line ad equal to line bc. If the angles of intersection still remain as right angles. The four lines form a rectangle.
Solving Primary School Mathematics 