2 VocabularyA circle is the set of all points in a plane that are equidistant from a given point called the center of the circle.A radius is a segment whose endpoints are the center and any point on the circle.
3 Vocabulary A chord is a segment whose endpoints are on a circle. A diameter is a chord that contains the center of the circle.The diameter is the longest chord a circle has.
4 Vocabulary A secant is a line that intersects a circle in two points. A tangent is a line in the plane of a circle that intersects the circle in exactly one point, the point of tangency.
6 VocabularyTheorem 6.1:In a plane, a line is tangent to a circle if and only if the line is perpendicular to a radius of the circle at its endpoint on the circle.
7 VocabularyTheorem 6.2:Tangent segments from a common external point are congruent.
8 Example 1:Tell whether the line, ray, or segment is best described as a radius, chord, diameter, secant, or tangent of circle P.
9 Example 2:Use the diagram to find the given lengths.
10 Example 3:Tell how many common tangents the circles have and draw them.
11 Example 4:RS is tangent to circle C at S and RT is tangent to circle C at T.Find the value of x.
12 Example 5:In the diagram, BC is a radius of circle C. Determine whether AB is tangent to circle C. Explain.
13 Example 6:In the diagram, B is a point of tangency. Find the radius r of circle C.**Remember we know that the radius is perpendicular to the tangent**This makes a RIGHT triangle!So we can use Pythagorean theorem to solve for r.