Mathematics for IGCSE & O level - Circle Theorems (Section 2 - No. 37)
What is the necessary and sufficient condition for a quadrilateral to be cyclic?
Its opposite angles are supplementary.
Its diagonals are equal.
All its angles are right angles.
Its opposite sides are parallel.
Paskaidrojums
A quadrilateral is cyclic if and only if its opposite angles are supplementary.