Page 154 - Math Course 2 (Book 2)

Lines of Fit

Make Predictions from an Equation
Step 2
Next, find the y-intercept.
Examples

y = mx + b Slope-intercept form

INTERNET Replace (x, y) with
The scatter plot shows the number of U.S. house- 10 = 6(1995) + b (1995,10) and m with 6.
holds (millions) with Internet access. Write an
equation in slope-intercept form for the line of fit. –11,960 = b Simplify.

Step 1
First, select two points on the line and find the Step 3
slope. Notice that the two points chosen are not Write the equation.
original data points. We have chosen (1995, 10)
and (1999, 34). y = mx + b Slope-intercept form

40 y = 6x + (–11,960) Replace m with 6 and b
U.S. Households with Internet Access (millions) 30 Predict the number of U.S. households that will
with –11,960.
35

y = 6x – 11,960
Answer
25

20
have internet in the year 2010.
15
Write the equation of the
10
y = 6x – 11,960
5
Replace x with 2010.

0 ‘94 ‘95 ‘96 ‘97 ‘98 ‘99 ‘00 y = 6(2010) – 11,960 line of fit.
Year y = 100 Simplify.

y y
__
m = 2 1 Definition of slope
x __ x Answer 100 million households
1
34 – 10 (x , y ) = (1995, 10)
m = 1 1
1999 – 1995 (x , y ) = (1999, 34)
2
2
24
m = or 6 Simplify.
4

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