Circle Theorems 3 - The Alternate Segment Theorem

This applet investigates the Alternate Segment Theorem

Author and programmer: Ron Barrow

UK Years 10-11, Ages 14-16, KS4, Higher GCSE Mathematics - Geometry, Shape and Space


Instructions below   Waldomaths video    See also:    2 Circle Theorems   2 More Circle Theorems   Circles and Tangents   Circles and Isosceles Triangles   Circles - Intersecting Chords   Circles - Radii and Chords   Parts of Circles

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How to Use this Applet

The line PQ is a tangent to the circle, touching the circle only once at the point A. You can move the points A, B and C around by clicking them and dragging them with your mouse. As you do so, look carefully at the size of the angles. There are different colours to help you. The sizes of the angles follow an important rule (theorem), which you can see by clicking "Show Theorem" at the bottom. Try not to do this - try to work the rule out by yourself! Enjoy yourself while you practise and learn this theorem by name.