Circle Theorems 1 10C3 01.02.12
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Transcript of Circle Theorems 1 10C3 01.02.12
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SFR Lesson NotesThe Winston Churchill School
Circle Theorems
Geometry
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38o
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76o
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70o
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65o
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Starter
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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 semicircle are 90o
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Angles in a semicircle:
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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
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Cyclic Quadrilateral
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