[" Theoriem "12.11" : The sum of either pair of "6%" ( ) "6y_(C)/2" and "B" .A an "],[" quadritiateral is "180^(@)" ."],[" In fact,the converse of this theorem,which is stated below is also true."],[" Theorem "12.12" : If the sum of a pair of opposite angles of a quadrilare "],[" 180's the quadrilateral is cyclic."],[" You can see the truth of this theorem by following a method similar to the meth."]