2 Objectives Find the lengths of segments of chords. Find the lengths of segments of tangents and secants.
3 Finding the Lengths of Chords When two chords of a circle intersect, each chord is divided into two segments which are called segments of a chord. There are several possible cases.
4 Theorem 9.14If two chords intersect in the interior of a circle, then the product of the lengths of the segments of one chord is equal to the product of the lengths of the segments of the other chord.EA • EB = EC • ED
5 Finding Segment Lengths Chords ST and PQ intersect inside the circle. Find the value of x.RQ • RP = RS • RTUse Theorem 9.14Substitute values.9 • x = 3 • 69x = 18x = 2Simplify.Divide each side by 9.
6 Using Segments of Tangents and Secants In the figure shown, PS is called a tangent segment because it is tangent to the circle at an end point. Similarly, PR is a secant segment and PQ is the external segment of PR.
7 Theorem 9.15If two secant segments share the same endpoint outside a circle, then the product of the length of one secant segment and the length of its external segment equals the product of the length of the other secant segment and the length of its external segment.EA • EB = EC • ED
8 Theorem 9.16If a secant segment and a tangent segment share an endpoint outside a circle, then the product of the length of the secant segment and the length of its external segment equal the square of the length of the tangent segment.(EA)2 = EC • ED
9 Finding Segment Lengths Find the value of x.RP • RQ = RS • RTUse Theorem 10.169•(11 + 9)=10•(x + 10)Substitute values.180 = 10x + 100Simplify.80 = 10xSubtract 100 from each side.8 = xDivide each side by 10.
10 Note:In Lesson 10.1, you learned how to use the Pythagorean Theorem to estimate the radius of a circle. Example 3 shows you another way to estimate the radius of a circular object.
11 Estimating the radius of a circle Aquarium Tank. You are standing at point C, about 8 feet from a circular aquarium tank. The distance from you to a point of tangency is about 20 feet. Estimate the radius of the tank.
12 Use Theorem 10.17(CB)2 = CE • CDSubstitute values.(20)2 8 • (2r + 8)Simplify.400 16r + 64Subtract 64 from each side.336 16rDivide each side by 16.21 rSo, the radius of the tank is about 21 feet.