Tangents of a Circle

OBJECTIVE: to discover the two properties of tangency
DEFINITION: A line is TANGENT if and only if it intersects a circle in exactly one point.
INSTRUCTIONS: Move the blue points around and observe the relationship beteen the green circle and the tangent lines.

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What can you conclude about the line segments CF and CE?
Are they congruent? Why?
What kind of relationship exists between the tangent line and the radius?

Allison Mumford, Created with GeoGebra