Grade 9 · Geometry
Circle Geometry
Circles are rich with hidden relationships. The angle inscribed in a semicircle is always 90° — a theorem students can discover by measuring and then prove. Tangent lines are perpendicular to the radius at the point of contact. These properties connect geometry, measurement, and deductive reasoning in a way that few other topics do.
LESSON VIDEO
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Lesson video
A short walkthrough to play in class or assign for flipped/at-home viewing.
WHAT STUDENTS WILL LEARN
✓Identify and apply properties of chords, tangents, and arcs
✓Apply the inscribed angle theorem
✓Prove and apply properties: angle in a semicircle, tangent-radius relationship
✓Solve problems using circle geometry theorems