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Videos to help GCSE Maths students learn the circle theorems.

• Angle subtended at the centre of a circle is twice the angle at the circumference.

• The angle between a radius and a tangent is 90 degrees.

• The angle at the centre is twice the angle at the circumference.

• Angles in the same segment are equal.

• The angle in a semi-circle is always 90 degrees.

• The opposite angles in a cyclic quadrilateral always add up to 180 degrees.

• The angle between a circle and a tangent is equal to the angle in the alternate segment.

• The lengths from where two tangents touch a circle to where they meet each other are equal.

Circle Theorem Basic definitions:

Chord, segment, sector, tangent, cyclic quadrilateral.

Theorem: Angle subtended at the centre of a circle is twice the angle at the circumference.

The angle between a radius and a tangent is 90 degrees.

The angle at the centre is twice the angle at the circumference.

Angles in the same segment are equal.

The angle in a semi-circle is always 90 degrees.

The opposite angles in a cyclic quadrilateral always add up to 180 degrees.

The angle between a circle and a tangent is equal to the angle in the alternate segment.

The lengths from where two tangents touch a circle to where they meet each other are equal.

You can use the Mathway widget below to practice Algebra or other math topics. Try the given examples, or type in your own problem. Then click "Answer" to check your answer.