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Geometry B Chapter 10

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Geometry BChapter 10

Segment Relationships in Circles

Objectives

Find the lengths of segments formed by lines that intersect circles.

Use the lengths of segments in circles to solve problems.

Warm Up

Solve for x.

1.

2. 3x = 122

3. BC and DC are tangent

to A. Find BC.

4

48

14

Vocabulary

secant segment

external secant segment

tangent segment

In 1901, divers near the Greek island of Antikythera discovered several fragments of ancient items. Using the mathematics of circles, scientists were able to calculate the diameters of the complete disks.

J

Example 1: Applying the Chord-Chord Product Theorem

Find the value of x and the length of each chord.

10(7)= 14(x)

70 = 14x

5 = x

EF = 10 + 7 = 17

GH = 14 + 5 = 19

In Your Notes! Example 1

Find the value of x and the length of each chord.

8(x) = 6(5)

8x = 30

x = 3.75

AB = 6 + 5 = 11

CD = 3.75 + 8 = 11.75

Example 2: Art Application

The art department is contracted to construct a wooden moon for a play. One of the artists creates a sketch of what it needs to look like by drawing a chord and its perpendicular bisector. Find the diameter of the circle used to draw the outer edge of the moon.

Example 2 Continued

8(d – 8) = 9 9

8d – 64 = 81

8d = 145

6 in.

In Your Notes! Example 2

What if…? Suppose the length of chord AB that the archeologists drew was 12 in. In this case how much longer is the disk’s diameter compared to the disk on p. 793?

6(6) = 3(QR)

12 = QR

12 + 3 = 15 = PR

A secant segmentis a segment of a secant with at least one endpoint on the circle. An external secant segmentis a secant segment that lies in the exterior of the circle with one endpoint on the circle.

Example 3: Applying the Secant-Secant Product Theorem

Find the value of x and the length of each secant segment.

112 = 64 + 8x

48 = 8x

6 = x

ED = 7 + 9 = 16

EG = 8 + 6 = 14

In Your Notes! Example 3

Find the value of z and the length of each secant segment.

351 = 169 + 13z

182 = 13z

14 = z

LG = 30 + 9 = 39

JG = 14 + 13 = 27

A tangent segmentis a segment of a tangent with one endpoint on the circle. ABand ACare tangent segments.

Example 4: Applying the Secant-Tangent Product Theorem

Find the value of x.

ML JL = KL2

20(5) = x2

100 = x2

±10 = x

The value of x must be 10 since it represents a length.

In Your Notes! Example 4

Find the value of y.

DE DF = DG2

7(7 + y) = 102

49 + 7y = 100

7y = 51

Lesson Quiz: Part I

1. Find the value of d and the length of each chord.

2. Find the diameter of the plate.

Lesson Quiz: Part II

3. Find the value of x and the length of each secant segment.

4. Find the value of a.