# Area of a quadrilateral Calculator

## Calculates the area and perimeter of a quadrilateral given four sides and two opposite angles.

side a
side b
side c
side d
sum of angles θ12

area S
perimeter L

 $\normal Bretschneider's\ formula \\\vspace{5}(1)\ area:\ S=\sqrt{(s{\small-}a)(s{\small-}b)(s{\small-}c)(s{\small-}d){\small-}abcd\cos^{\small2}\frac{\theta}{2}}\\\hspace{150} s={\large\frac{a+b+c+d}{2}}\\\vspace{5}(2)\ perimeter:\ L=2s=a+b+c+d$

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