How do you find an area of a four sided diagram?

Answer 1

Area = square root of {s1(s1-a)(s1-b)(s1-p)} + square root of {s2(s2-c)(s2-d)(s2-p)}

where a,b,c and d are the four sides of the quadrilateral, p is the diagonal separating the sides a,b from c,d, and s1 = (a+b+p)/2 and s2 = (c+d+p)/2