1. Using Segments and Congruence Midpoint Formula
Section 2.1
Using Segments and Congruence
Midpoint Formula

2. Objectives – What we’ll learn…
Apply the properties of real numbers to the measure of segments.

3. Segments
Where is B located?
Between A and C
Where is D located?
Not between A and C A B C D
For a point to be between two other points, all three points must be collinear. Segments can be defined using the idea of betweenness of points.

4. Measure of Segments What is a segment?C B A
What is a segment?
A part of a line that consists of two endpoints and all the points between them.
What is the measure of a segment?
The distance between the two endpoints.
In the above figure name three segments:
CB BA AC

5. Postulate 2-1 Ruler Postulate
The distance between points A and B, written as AB, is the absolute value of the difference of the coordinates of A and B.
Use |Absolute Value|!!! X Y
Since x is at -2 and Y is at 4, we can say the distance from X to Y or Y to X is:
-2 – 4 = 6 or 4 – (-2) = 6

6. Apply the Ruler Postulate
EXAMPLE 1
Apply the Ruler Postulate
Measure the length of ST to the nearest tenth of a centimeter.
SOLUTION
Align one mark of a metric ruler with S. Then estimate the coordinate of T. For example, if you align S with 2, T appears to align with 5.4.
ST = 5.4 – 2 = 3.4
Use Ruler Postulate.
The length of ST is about 3.4 centimeters.
ANSWER

7. Summary What do we use to find the distance between two points?
|Absolute Value|

8. Using Segments and Congruence Distance and Midpoint Formula
Section 2.2
Using Segments and Congruence
Distance and Midpoint Formula

9. Postulate 2-2 Segment Addition Postulate
If Q is between P and R, then
PQ + QR = PR.
If PQ +QR = PR, then Q is between P and R. 2x
4x + 6 R P Q
PQ = 2x QR = 4x + 6 PR = 60
Use the Segment Addition Postulate find the measure of PQ and QR.

10. Step 1:
PQ + QR = PR (Segment Addition) 2x + 4x + 6 = 60 6x + 6 = 60 6x = 54 x =9 PQ = 2x = 2(9) = 18 QR =4x + 6 = 4(9) + 6 = 42
Step 2:
Step 3:
Step 4:

11. Steps Draw and label the Line Segment.
Set up the Segment Addition/Congruence Postulate.
Set up/Solve equation.
Calculate each of the line segments.

12. Use the diagram to find GH.
EXAMPLE 3
Find a length
Use the diagram to find GH.
SOLUTION
Use the Segment Addition Postulate to write an equation. Then solve the equation to find GH.
FG + GH = FH
Segment Addition Postulate.
21 + GH = 36
Substitute 36 for FH and 21 for FG. = 15 GH
Subtract 21 from each side.

13. Compare segments for congruence
EXAMPLE 4
Compare segments for congruence
Plot J(– 3, 4), K(2, 4), L(1, 3), and M(1, – 2) in a coordinate plane. Then determine whether JK and LM are congruent.
SOLUTION
To find the length of a horizontal segment, find the absolute value of the difference of the x-coordinates of the endpoints.
JK = 2 – (– 3) = 5
Use Ruler Postulate.

14. EXAMPLE 4
Compare segments for congruence
To find the length of a vertical segment, find the absolute value of the difference of the y-coordinates of the endpoints.
LM = – 2 – 3 = 5
Use Ruler Postulate.
JK and LM have the same length. So, JK LM.
Remember when we speak of length the bar does not go over the letters but it does when we speak of congruence. = ~
ANSWER

15. Midpoint Formula: Finding the midpoint and endpoint.
Section 2.5
Midpoint Formula: Finding the midpoint and endpoint.

16. What is midpoint?
The midpoint M of PQ is the point between P and Q such that PM = MQ. P M Q
Endpoint: P
Endpoint: Q
Midpoint: M

17. How do you find the midpoint?
On a number line, the coordinate of the midpoint of a segment whose endpoints have coordinates a and b is (a + b)/2.
Find the AVERAGE!

18. Examples: 1.) Find the midpoint of AC: -5 6 Endpoint: -5 Endpoint: 6-5 6
Endpoint: -5
Endpoint: 6
(Finding Average of two numbers)
(-5 + 6)/2
Midpoint: 1/2

19. 2.) If M is the midpoint of AZ,
AM = 3x + 12 and MZ = 6x –9; find the measure of AM and MZ.
AM = MZ (Def. of Midpoint)
3x + 12 = 6x – 9
21 = 3x
X = 7
AM =3x + 12 =3(7) + 12 = 33
MZ = 6x – 9 = 6(7) – 9 = 33
Step 2:
Step 3:
Step 4:

20. Steps of finding midpoint.
Find midpoint of (-3, 7) and (8, -4).
Endpoint 1: ( -3 , )
Endpoint 2: ( 8 , )
Midpoint: ( , )
(Average of x)
(Average of y)

21. Steps Draw and label the Line Segment. Set up the GEOMETRY Expression.
a) Segment Addition Postulate
b) Definition of Midpoint
c) Definition of Congruence
3. Set up/Solve equation.
4. Calculate each of the line segments.

22. Steps of finding Endpoint!
Find the other endpoint with endpoint (-5, 6) & midpoint (3/2, 5).
Endpoint 1: ( -5 , )
Endpoint 2: ( x , y )
Midpoint: ( , )
(8, 4)
Solve Equations:

23. Steps of finding Midpoint:
Write down the order pair.
Find the AVERAGE of the x1 and x2.
(x1 + x2)/2 =
Find the AVERAGE of the y1 and y2.
(y1 + y2) /2 =
Write them as an order pair.

24. Example: 1.) Find the midpoint, M, of A(2, 8) and B(4, -4).
y = (8 + (-4)) ÷ 2 = 2
M = (3, 2)
2.) Find M if N(1, 3) is the midpoint of MP where the coordinates of P are (3, 6).
M = (-1, 0)
Find AVERAGE of x ->
<-Find AVERAGE of y

25. Q. How do you find the midpoint of 2 ordered pairs?
A. In a coordinate plane, the coordinates of the midpoint of a segment whose endpoints have coordinates (x1, y1) and (x2, y2) are ((x1 + x2)/2), (y1 + y2)/2)

26. EXAMPLE 3
Use the Midpoint Formula
a. FIND MIDPOINT The endpoints of RS are R(1,–3) and S(4, 2). Find the coordinates of the midpoint M.

27. Use algebra with segment lengths
EXAMPLE 2
Use algebra with segment lengths
Point M is the midpoint of VW . Find the length of VM .
ALGEBRA
SOLUTION
STEP 1
Write and solve an equation. Use the fact that VM = MW.
VM = MW
Write equation.
4x – 1 = 3x + 3
Substitute.
x – 1 = 3
Subtract 3x from each side.
x = 4
Add 1 to each side.

28. EXAMPLE 2
Use algebra with segment lengths
STEP 2
Evaluate the expression for VM when x = 4.
VM = 4x – 1 = 4(4) – 1 = 15
So, the length of VM is 15.
Check: Because VM = MW, the length of MW should be 15. If you evaluate the expression for MW, you should find that MW = 15.
MW = 3x + 3 = 3(4) +3 = 15

29. Bisectors What is a segment bisector?
- Any segment, line, or plane that intersects a segment at its midpoint. A B C M N
If B is the midpoint of AC, then MN bisects AC.

30. Point T is the midpoint of XY . So, XT = TY = 39.9 cm.
EXAMPLE 1
Find segment lengths
In the skateboard design, VW bisects XY at point T, and XT = 39.9 cm. Find XY.
Skateboard
SOLUTION
Point T is the midpoint of XY . So, XT = TY = 39.9 cm.
XY = XT + TY
Segment Addition Postulate =
Substitute.
= 79.8 cm
Add.

31. GUIDED PRACTICE
for Examples 1 and 2
In Exercises 1 and 2, identify the segment bisector of PQ . Then find PQ. 2.
line l ; 11 5 7
ANSWER

32. Distance Formula
The Distance Formula was developed from the Pythagorean Theorem
Where d = distance
x =x-coordinate and y=y-coordinate