IGCSE Maths / Circle theorems

Opposite angles of a cyclic quadrilateral

Edexcel International GCSE Maths (4MA1), chapter 17: Circle theorems, specification point 4.6c. Part of the full course.

Read the revision notes · IGCSE Maths past papers

In a cyclic quadrilateral, each pair of opposite angles adds up to 180°. You can use this rule to find missing angles, including angles written with an unknown such as x.

More lessons in Circle theorems

• Parts of a circle and cyclic quadrilaterals
• Tangent and radius, and two tangents from a point
• The angle at the centre is twice the angle at the circumference
• The angle in a semicircle
• Angles in the same segment
• The alternate segment theorem
• Using the alternate segment theorem in a reasoning chain
• Reasoning chains with circle theorems
• Multi-step circle theorem problems
• Intersecting chords inside a circle
• Intersecting chords from a point outside the circle