The circle theorems are a number of rules or facts we happen to know about the angles in squares and triangles that are drawn inside of circles. You are expected to memorise them.

The word ‘subtend’ or ‘subtended’ is an awkward one that crops up a lot in these theorems. For example, the arrow theorem in words is “The angle subtended by a chord at the centre is twice the angle subtended at the circumference.”

Subtended just means ‘created’. Wherever you read the word ‘subtend ‘or ‘subtended’, replace it with ‘create’ or ‘created’.

In your GCSEs, you'll find eight theorems of mathematics in total:

Arrow theorem Bow theorem Angles in semi-circle
Alternate segment theorem
Radius-tangent theorem
Dual tangent theorem
Cyclic quadrilateral theorem
Radius-chord theorem

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