In geometry, a quadrilateral, quadrangle or tetragon is a polygon with four sides, with all it's corners adding up to 360° or 2π radians.

Types

The following are special cases of the quadrilateral:

• Trapezium
• Trapezoid
• Parallelogram
• Rectangle
• Rhombus
• Square
• Kite

Area

Brahmagupta's formula finds the area of any quadrilateral given the lengths of the sides is

${\displaystyle A= \sqrt{\frac{(a^2+b^2+c^2+d^2)^2+8abcd-2(a^4+b^4+c^4+d^4)}{16}}}$