Mathematics for IGCSE & O level - Circle Theorems (Section 2 - No. 42)
If a quadrilateral is inscribed in a circle, what must be true about its opposite angles?
They are equal.
They are complementary.
They are supplementary.
They are always right angles.
Explicação
Opposite angles of a cyclic quadrilateral are supplementary, meaning they add up to 180 degrees.