inscriptable quadrilateral

A quadrilateral which has an incircle, i.e., one for which a single circle can be constructed which is tangent to all four sides. Opposite sides of such a quadrilateral satisfy s = a + c = b + d, where s = 1/2(a + b + c + d) is the semiperimeter, and the area is A = r s, where r is the inradius.

bicentric quadrilateral | cyclic quadrilateral | incircle | quadrilateral | rhombus | tangential triangle