8. M is the midpoint of AB. Find AM and MB.
Example 1
Find Segment Lengths
M is the midpoint of AB. Find AM and MB.
SOLUTION
AM = MB = 2 1
· AB =
· 26 13
ANSWER
AM = 13 and MB = 13. 8

9. P is the midpoint of RS. Find PS and RS.
Example 2
Find Segment Lengths
P is the midpoint of RS. Find PS and RS.
SOLUTION
P is the midpoint of RS, so PS = RP. Therefore, PS = 7.
RS = = = 14
2 · RP
2 · 7
ANSWER
PS = 7 and RS = 14. 9

10. Checkpoint
Find Segment Lengths
Find DE and EF. 1.
Find NP and MP. 2.

11. Checkpoint 1. Find DE and EF. ANSWER DE = 9; EF = 9 2. Find NP and MP.
Find Segment Lengths
Find DE and EF. 1.
ANSWER
DE = 9; EF = 9
Find NP and MP. 2.
ANSWER
NP = 11; MP = 22

12. Line l is a segment bisector of AB. Find the value of x.
Example 3
Use Algebra with Segment Lengths
Line l is a segment bisector of AB. Find the value of x.
SOLUTION
AM = MB
5x = 35 5 5x = 35
x = 7
Check your solution by substituting 7 for x.
5x = 5(7) = 35
CHECK 12

16. Find the coordinates of the midpoint of AB.
Example 4
Use the Midpoint Formula
Find the coordinates of the midpoint of AB.
A(1, 2), B(7, 4) a.
A(–2, 3), B(5, –1) b.
SOLUTION
First make a sketch. Then use the Midpoint Formula. a.
Let (x1, y1) = (1, 2) and (x2, y2) = (7, 4).
M = 2
x1 + x2 ,
y1 + y2 = 2
1 + 7 ,
2 + 4
= (4, 3) 16

17. Let (x1, y1) = (–2, 3) and (x2, y2) = (5, –1). M = 2 x1 + x2 , y1 + y2
Example 4
Use the Midpoint Formula b.
Let (x1, y1) = (–2, 3) and (x2, y2) = (5, –1).
M = 2
x1 + x2 ,
y1 + y2 = 2
–2 + 5 ,
3 +(– 1) 2 3
, 1 = 17

18. Sketch PQ. Then find the coordinates of its midpoint.
Checkpoint
Use the Midpoint Formula
Sketch PQ. Then find the coordinates of its midpoint.
P(2, 5), Q(4, 3) 3.
P(0, –2), Q(4, 0) 4.
P(–1, 2), Q(–4, 1) 5.

19. Sketch PQ. Then find the coordinates of its midpoint.
Checkpoint
Use the Midpoint Formula
Sketch PQ. Then find the coordinates of its midpoint.
P(2, 5), Q(4, 3) 3.
ANSWER
(3, 4)
P(0, –2), Q(4, 0) 4.
ANSWER
(2, –1)
ANSWER
– , 2 5 3
P(–1, 2), Q(–4, 1) 5.

20. Review

21. Use the figure at the right.1.
Use a protractor to approximate the measure of ABC.
ANSWER
30° 2.
Use your answer to Exercise 1 and the Angle Addition Postulate to find the measure of ABD.
ANSWER
90° 3.
Classify each of the three angles shown in the figure as acute, right, obtuse, or straight.
ANSWER
ABC is acute, CBD is acute, and ABD is right.

22. Hw 2.1