Circle theorems lesson 7

A complete lesson on the theorem that tangents from a point are equal.

Assumes pupils can already use the theorems that:

1. The angle at the centre is twice the angle at the circumference
2. The angle in a semicircle is 90 degrees
3. Angles in the same same segment are equal
4. .Opposite angles in a cyclic quadrilateral sum to 180 degrees
5. A tangent is perpendicular to a radius
6. Angles in alternate segments are equal
   so that more varied questions can be asked. Please see my other resources for lessons on these theorems.

Activities included:

Starter:
Instructions for pupils to discover the theorem, by drawing tangents and measuring.

Main:

• Slides to clarify why this theorem usually involves isosceles triangles.
• Related examples, finding missing angles.
• A set of eight questions using the theorem (and usually another theorem or angle fact).
• Two very sneaky extension questions.

Plenary:
An animation of the proof without words, the intention being that pupils try to describe the steps.

Printable worksheets and answers included.

Please review if you buy, as any feedback is appreciated!