In geometry, a quadrilateral, quadrangle or tetragon is a polygon with four sides.
The following are special cases of the quadrilateral:
Brahmagupta's formula finds the area of any quadrilateral given the lengths of the sides is
A = ( a 2 + b 2 + c 2 + d 2 ) 2 + 8 a b c d − 2 ( a 4 + b 4 + c 4 + d 4 ) 16 {\displaystyle A= \sqrt{\frac{(a^2+b^2+c^2+d^2)^2+8abcd-2(a^4+b^4+c^4+d^4)}{16}}}
