10.6 Segment Relationships in Circles - Big Ideas Learning
10.6 Segment Relationships in Circles
REASONING ABSTRACTLY
To be proficient in math, you need to make sense of quantities and their relationships in problem situations.
Essential Question What relationships exist among the
segments formed by two intersecting chords or among segments of two
secants that intersect outside a circle?
Segments Formed by Two Intersecting Chords
Work with a partner. Use dynamic geometry software.
a. Construct two chords B--C and D--E Sample
that intersect in the interior of a circle at a point F.
B
b. Find the segment lengths BF, CF, DF, and EF and complete the table. What do you observe?
E F
BF CF BF CF
A
C
D
DF EF DF EF
c. Repeat parts (a) and (b) several times. Write a conjecture about your results.
Secants Intersecting Outside a Circle
Work with a partner. Use dynamic geometry software.
a. Construct two secants BC and BD
that intersect at a point B outside a circle, as shown.
Sample
b. Find the segment lengths BE, BC,
BF, and BD, and complete the table.
E
What do you observe?
B
BE BC BE BC
F
C A
BF BD BF BD
D
D
9
18
A
E
F
8
C
c. Repeat parts (a) and (b) several times. Write a conjecture about your results.
Communicate Your Answer
3. What relationships exist among the segments formed by two intersecting chords or among segments of two secants that intersect outside a circle?
4. Find the segment length AF in the figure at the left.
Section 10.6 Segment Relationships in Circles 613
10.6 Lesson
Core Vocabulary
segments of a chord, p. 614 tangent segment, p. 615 secant segment, p. 615 external segment, p. 615
What You Will Learn
Use segments of chords, tangents, and secants.
Using Segments of Chords, Tangents, and Secants
When two chords intersect in the interior of a circle, each chord is divided into two segments that are called segments of the chord.
Theorem
Segments of Chords Theorem If 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.
Proof Ex. 19, p. 618
C
A
E
B
D
EA EB = EC ED
Using Segments of Chords
Find ML and JK.
M
x + 2
K
N x
x + 4 x + 1
J
SOLUTION
NK NJ = NL NM x (x + 4) = (x + 1) (x + 2)
x2 + 4x = x2 + 3x + 2
L
Segments of Chords Theorem Substitute. Simplify.
4x = 3x + 2
Subtract x2 from each side.
x = 2
Subtract 3x from each side.
Find ML and JK by substitution.
ML = (x + 2) + (x + 1)
JK = x + (x + 4)
= 2 + 2 + 2 + 1
= 2 + 2 + 4
= 7
= 8
So, ML = 7 and JK = 8.
Monitoring Progress
Find the value of x.
1. x6 43
Help in English and Spanish at
2.
2
4 x + 1
3
614 Chapter 10 Circles
Core Concept
Tangent Segment and Secant Segment
R
A tangent segment is a segment that
external segment Q
is tangent to a circle at an endpoint. A secant segment is a segment that
P
secant segment
contains a chord of a circle and has exactly one endpoint outside the
tangent segment S
circle. The part of a secant segment that is outside the circle is called an external segment.
PS is a tangent segment. PR is a secant segment. PQ is the external segment of PR.
Theorem
Segments of Secants Theorem If two secant segments share the same endpoint outside a circle, then the product of the lengths of one secant segment and its external segment equals the product of the lengths of the other secant segment and its external segment.
Proof Ex. 20, p. 618
B A E
C D
EA EB = EC ED
Using Segments of Secants
Find the value of x.
R
SOLUTION
RP RQ = RS RT 9 (11 + 9) = 10 (x + 10)
180 = 10x + 100 80 = 10x 8 = x
Q 11 9P 10 S x T
Segments of Secants Theorem Substitute. Simplify. Subtract 100 from each side. Divide each side by 10.
The value of x is 8.
Monitoring Progress
Find the value of x.
3. 9 6
x 5
Help in English and Spanish at
4.
3 x+2
x+1 x-1
Section 10.6 Segment Relationships in Circles 615
Theorem
Segments of Secants and Tangents Theorem If a secant segment and a tangent segment share an endpoint outside a circle, then the product of the lengths of the secant segment and its external segment equals the square of the length of the tangent segment.
Proof Exs. 21 and 22, p. 618
A
E C D
EA2 = EC ED
ANOTHER WAY
IsnegEmxaemntpsleQ--S3,aynoduQ--cTan. draw
R
16
Q
x S8
T
Because RQS and RTQ intercept the same arc, they are congruent. By the Reflexive Property of Congruence, QRS TRQ. So, RSQ RQT by the AA Similarity Theorem. You can use this fact to write and solve a proportion to find x.
Using Segments of Secants and Tangents
Find RS.
R
SOLUTION
RQ2 = RS RT 162 = x (x + 8)
256 = x2 + 8x
Segments of Secants and Tangents Theorem
Substitute.
Simplify.
0 = x2 + 8x - 256
x = -- -8 ? -- 8-- 2 2-(14)(1-- -- )(-256)
x = -4 ? 4-- 17
Write in standard form. Use Quadratic Formula. Simplify.
Use the positive solution because lengths cannot be negative.
So, x = -4 + 4-- 17 12.49, and RS 12.49.
16
x S
Q
8 T
Finding the Radius of a Circle
Find the radius of the aquarium tank.
SOLUTION
CB2 = CE CD
202 = 8 (2r + 8)
400 = 16r + 64 336 = 16r 21 = r
Segments of Secants
Dr
and Tangents Theorem
Substitute.
Simplify.
Subtract 64 from each side.
Divide each side by 16.
So, the radius of the tank is 21 feet.
B 20 ft
r E 8 ftC
Monitoring Progress
Find the value of x.
5.
6.
31
x
Help in English and Spanish at
5x 7
7.
x
10 12
8. WHAT IF? In Example 4, CB = 35 feet and CE = 14 feet. Find the radius of the tank.
616 Chapter 10 Circles
10.6 Exercises
Dynamic Solutions available at
Vocabulary and Core Concept Check
1. VOCABULARY The part of the secant segment that is outside the circle is called a(n) _____________.
2. WRITING Explain the difference between a tangent segment and a secant segment.
Monitoring Progress and Modeling with Mathematics
In Exercises 3?6, find the value of x. (See Example 1.)
3.
4.
12 10
6 x
x - 3 10 18
9
5.
x 8 x + 8
6
6.
15 2x 12
x + 3
In Exercises 7?10, find the value of x. (See Example 2.)
7.
8.
5
10 6
7 x
x
8
4
9.
10.
5 4
x + 4
x - 2
45 x 27
50
In Exercises 11?14, find the value of x. (See Example 3.)
11.
12.
x
24
7
9
12
x
13.
x 12
14.
x + 4
3
2
x
15. ERROR ANALYSIS Describe and correct the error in finding CD.
F 3A
5
B
4 D C
CD DF = AB AF CD 4 = 5 3 CD 4 = 15
CD = 3.75
16. MODELING WITH MATHEMATICS The Cassini
spacecraft is on a mission in orbit around Saturn until
September 2017. Three of Saturn's moons, Tethys,
Calypso, and Telesto, have nearly circular orbits of
radius 295,000 kilometers. The diagram shows the
positions of the moons and the spacecraft on one
oCfaCssainssiitnoi'Ts emthiysssiownhse. nFAi--nDd
the distance DB is tangent to the
from circular
orbit. (See Example 4.)
Tethys B
Calypso C
83,000 km
D Cassini
Saturn
203,000 km Telesto A
Section 10.6 Segment Relationships in Circles 617
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