Edges of triangle is given by equations a_ix+b_iy+c_i=0\ (i=1,2,3).
Prove that the area P of triangle is given with
<br />
P=\frac{{\Delta}^2}{2|{\Delta}_1{\Delta}_2{\Delta}  _3|} where \Delta=\vmatrix<br />
a_1&b_1&c_1\\<br />
a_2&b_2&c_2\\<br />
a_3&b_3&c_3<br />
\endvmatrix ,<br />

and \Delta_i are algebric complements of elements c_i