daca diagonalele AC =a si BD = b ACП BD = { O }
in Δ ABO ; AB = AC /2 + DB /2 = AC /2 - BD /2 = ( a - b) / 2
in Δ BOC ; BC = BD /2 + AC /2 = ( b + a) /2
in Δ COD ; CD = CA /2 + BD /2 = - AC /2 + BD /2 = ( - a +b) /2
in Δ DOA ; DA = DB /2 + CA /2 = - BD /2 - AC /2 = ( - b - a) /2