Circle Vocabulary

A dynamic illustration of some of the terms we use to talk about circles. Click the term and describe what you see. How would you define the idea with words? There's also a couple things to notice about some of the special properties that angles in circles.

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Math 9: Tangent to a Circle

Move Point A so line segment AB is tangent (just touching) the circle at point D. What do you notice about the angle?

The Rule: A tangent to a circle is perpendicular to the radius at the point of tangency.