Mathematics for IGCSE & O level - Circle Theorems (Section 2 - No. 30)

Which of the following must be true in a circle?

Equal chords are equidistant from the center.

Chords that are equidistant from the center are equal in length.

The angle in a semicircle is a right angle.

Opposite angles of a cyclic quadrilateral are equal.

These are standard circle theorems. Only the last option is incorrect; they are supplementary not equal.