Circle Properties

What you'll learn

Angle properties of circles: semicircle, centre vs circumference, same segment, cyclic quadrilaterals, and tangents.

• The angle in a semicircle is 90 degrees
• The angle at the centre is twice the angle at the circumference, on the same arc
• Angles in the same segment are equal
• Opposite angles of a cyclic quadrilateral sum to 180 degrees
• A tangent is perpendicular to the radius at the point of contact
• Two tangents from the same external point are equal in length