Key Concepts: Tangents

Definition

A tangent to a circle is a line in the plane of the circle that intersects the circle at exactly one point, the point of tangency.

Key Theorems

• A tangent is perpendicular to the radius drawn to the point of tangency.
• If two segments from the same exterior point are tangent to a circle, then they are congruent.

Common Tangents

• Common internal tangent: intersects the segment joining the centers of two circles.
• Common external tangent: does not intersect the segment joining the centers.