The definition of a rectangle is that it has 2 pairs of congruent opposite sides.
When a rhombus has to be equal in ALL sides.
Another proof is that a rectangle have 4 90 degree angles. Whilst a rhombus DOES not have a single right angle no matter the case.
A more advanced proof would be if the diagonals would be perpendicular or if the diagonals would bisect two angles of a rhombus. Whilst a rectangle’s diagonal are only congruent, not neccisalry perpendicular or bisects two angles.
Step-by-step explanation: A rectangle is a parallelogram with all its interior angles being 90 degrees. A rhombus is a parallelogram with all its sides equal. This means that for a rectangle to be a rhombus, its sides must be equal.