NAME ______________________________________________ DATE
8-8 Best-Fit Lines
____________ PERIOD _____
(Pages 409–413)
When collecting real-life data, the points rarely form a straight line; however,
the points may approximate a linear relationship. In this case, a best-fit line
may be used. A best-fit line is a line that is drawn close to all of the points in
the data. In short, it is the line that best fits the points. Best-fit lines help us
to write equations for a set of data and predict what may happen if the data
continues on the same trend.
Example
Age
Height in Inches
10
57
11
60
12
62
y
13
63
68
67
66
65
64
63
62
61
60
59
58
57
56
55
14
66.5
15
68
The table shows Tisha’s height at various ages. Use
the information to make a scatter plot, draw a best-fit
line, and write an equation for the data.
y y
x2 x1
2
1
m Select two points to find the slope.
62 68
m
x1 15, y1 68, x2 12, y2 62
m2
The slope is 2.
12 15
y mx b
O
x
10 11 12 1314 15
Use the slope-intercept form.
62 2.12 b
Replace m with 2 and use any point.
38 b
Solve for b.
y 2x 38
Replace m and b in the equation.
Practice
Use the table that shows the number of goals Pierre scored
playing hockey to answer problems 1–4.
Year
Goals
1997
26
1. Using the data from 2001 and 1997, find the slope of the line.
1998
24
2. With your answer from problem 1 and the point (2000, 19), write
an equation for the line in slope-intercept form.
1999
20
2000
19
3. Using your answer from problem 2, how many goals should
Pierre score in 2004?
2001
15
4. Standardized Test Practice What would have been the equation for
problem two if the given information was the answer to problem 1 and
the point (1998, 24)?
11
1
11
1
11
1
11
1
A y
x 5518 B y 5518 C y x 5518 D y x 5518 4
2
4
2
4
11
2. y x 5519 3. 8 4. A
©
Glencoe/McGraw-Hill
68
4
2
4
2
11
Answers: 1. m 4
Glencoe Pre-Algebra