Formula
$$A=\dfrac{1}{2} \left[(x_1-x_2)(y_1+y_2)+(x_2-x_3)(y_2+y_3)+(x_3-x_4)(y_3+y_4)+(x_4-x_1)(y_4+y_1) \right]$$
Variables
A(x1,y1)
→
Quadrilateral vertice
B(x2,y2)
→
Quadrilateral vertice
C(x3,y3)
→
Quadrilateral vertice
D(x4,y4)
→
Quadrilateral vertice