SFR Lesson Notes The Winston Churchill School
Circle Theorems Geometry
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
Need help? 足 mymaths: Circle Theorems 足 online textbook: pages 138 足 141
Circle Theorems 1 - Angles in a semi-circle - Cyclic Quadrilateral