Inscribed angle subtended by the diameter

If an angle is inscribed in a circle and its sides pass through the endpoints of a diameter, then the angle is always a right angle (90 degrees). This is known as Thales' Theorem.

Important properties

• Any inscribed angle subtended by the diameter is a right angle.

• This property holds for any point on the circle except the endpoints of the diameter.

• It is a special case of the general inscribed angle theorem, where the arc subtended is a semicircle.