Quadrilateral

In geometry, a quadrilateral, quadrangle or tetragon is a polygon with four sides.

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

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