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GeoGebra

Circles

Author:pirsquared
Topic:Circle

Key Facts

You must learn the following:
  • The equation of a circle with centre  and radius is given by
  • If the equation is given in expanded form, eg. , then it is necessary to complete the square before identifying the centre and radius:
Image

Test Yourself - Equation of a Circle

Relevant Circle Theorems

Relevant Circle Theorems
A tangent to the circle will meet the radius at a right-angle. (Gradient of radius is usually calculated easily from a known point on the circle, P, and the centre of the circle, C).
The length from a point along a tangent can form a right-angled triangle.
The length from a point along a tangent can form a right-angled triangle.
A chord will be [b]perpendicularly bisected [/b]by a specific radius.
A chord will be perpendicularly bisected by a specific radius.

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