A rectangle is a parallelogram in which two adjacent angles are equal or each angles is equal to 90°.

1. If P  is any point inside the rectangle, then 
   \(P{A^2} + P{C^2} = P{B^2} + P{D^2}\)
2. Area of a rectangle = \(ab\)
3. The diagonals are equal and bisect each other.
4. When \(a\) Rectangle is inscribed in a circle the diagonals become the diameters of the circle. 
5. If \(‘a’\) and \(‘b’\) are the two adjacent sides the diagonal is given by \(\sqrt {{a^2} + {b^2}} \)