# Rectangle area

A rectangle is a quadrangle in which all angles are right and equal to 90 degrees, and the opposite sides are parallel and equal in pairs.

**Area of a rectangle through its sides**

**Side а:**

**Side b:**

**Diagonal area of a rectangle**

**Diagonal d:**

**Angle between diagonals α:**

Rectangle properties

- A rectangle has opposite sides equal and parallel
- The sides of the rectangle are its heights
- The diagonals of the rectangle are equal, intersect, and the intersection is halved.
- The square of the diagonal of a rectangle is equal to the sum of the squares of its two adjacent sides (by the Pythagorean theorem)
- The rectangle is a parallelogram, its opposite sides are pairwise parallel
- A circle can be described around any rectangle, and the diagonal of the rectangle is equal to the diameter of the circumscribed circle, the radius is equal to the half-diagonal.