Question: what is the formula of area of cyclic quadrilateral?
Answer: Area. where s, the semiperimeter, is s = 12(a + b + c + d). This is a corollary of Bretschneider's formula for the general quadrilateral, since opposite angles are supplementary in the cyclic case. If also d = 0, the cyclic quadrilateral becomes a triangle and the formula is reduced to Heron's formula.