Circle theorems

By the end you’ll be able to

• Name the parts of a circle: radius, diameter, chord, tangent, arc, sector and segment
• Apply the circle theorems: angle at the centre is twice the angle at the circumference, angle in a semicircle is 90°, angles in the same segment are equal, and opposite angles of a cyclic quadrilateral add to 180° (Higher)
• Apply the tangent theorems (tangent perpendicular to radius, equal tangents from an external point), the perpendicular from the centre bisects a chord, and the alternate segment theorem (Higher)