Quadrangle area
A quadrilateral is a polygon with four vertices and four sides. No three vertices of a quadrangle lie on one straight line Distinguish between convex and non-convex quadrangles
. Diagonal of a quadrilateral d1
Diagonal of a quadrilateral d2
Angle between diagonals α
The formula for calculating the area of a quadrilateral, through the diagonals and the angle between them:
S=1/2⋅d1⋅d2⋅sinα∘
Side а
Side b
Side c
Side d
Angle between sides α°
Angle between sides β°
Formula for calculating the area of a quadrilateral in terms of its four sides and the angles between these sides: 
p – perimeter of a quadrilateral divided by two.