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SFR Lesson Notes The Winston Churchill School

Circle Theorems Geometry


1

3

x

x

70o

38o

2

4

x 76o

x 65o

Starter


Draw a circle. Draw a diameter and label it AB. Mark any point C on the circumference. Join A, B and C to form a triangle. Measure angle ACB. What do you find? Repeat these steps to establish a rule.

= Circle Theorem 1: Angles in a semi足circle are 90o


Angles in a semicircle:


Draw a circle. Mark any four points on the circumference and label them A, B, C and D. Join A, B, C and D to form a quadrilateral. Measure the angles inside the quadrilateral. Add the opposite angles together. What do you find? Repeat these steps to establish a rule. = Circle Theorem 2: Opposite angles in a cyclic quadrilateral + to 180o


Cyclic Quadrilateral


Need help? 足 mymaths: Circle Theorems 足 online textbook: pages 138 足 141


Circle Theorems 1 10C3 01.02.12  

Circle Theorems 1 - Angles in a semi-circle - Cyclic Quadrilateral

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