1. Cyclic quadrilateral Class IX Prepared by P.E.Venugopalan K.V.KELTRON NAGAR

2. Cyclic quadrilateral  A quadrilateral is called a cyclic quadrilateral if all the four vertices of it lie on a circle

3. Theorem (10.11)  The sum of either pair of opposite angles of a cyclic quadrilateral is 180° D C B A If ABCD is a cyclic quadrilateral,then (i) ∟A + ∟C =180° and (ii) ∟B + ∟D = 180°

4. Converse of Theorem 10.11  If the sum of a pair of opposite angles of a quadrilateral is 180°,the quadrilateral is cyclic(Theorem 10.12) A D C B ABCD is a cyclic quadrilateral if (i) ∟A + ∟C =180° Or (ii) ∟B + ∟D = 180°