1. Section 10-1
Tangents to Circles

2. Theorem 10-1
If a line is tangent to a circle, then the line is perpendicular to the radius drawn to the point of tangency.

3. l
Point of Tangency Q P
If l is tangent to Circle P at Q, then

4. Theorem 10-2
In the plane, if a line is perpendicular to a radius of a circle at its endpoint on the circle, then the line is tangent to the circle.

5. then l is tangent to Circle P at Q
Tangent line l Q P
If ,
then l is tangent to Circle P at Q

6. Theorem 10-3
If two segments from the same exterior point are tangent to a circle, then they are congruent.

7. and
are tangent to Circle Q A P Q B