### Theory:

A parallelogram whose each angle is a right angle is called a rectangle.
Now we are going to define a rectangle $$ABCD$$ as a quadrilateral is a parallelogram whose each interior angle is $$90°$$.

Thus, if $$ABCD$$ is a rectangle then $$AB=BC=CD=AD$$ and $$AB||CD$$ and $$BC||AD$$.
Important!
A rectangle has all the properties of a parallelogram with interior.
In a rectangle, the following properties are true:
1. The opposite sides are parallel and equal in length.
2. The interior angles of the rectangle is $$90°$$.
3. The diagonals are equal in measure and bisect each other.
4. The adjacent angles are supplementary.