# 2-4 Writing Linear Equations

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```					  2-4 Writing Linear Equations
Objective: To write an equation of a line in
slope intercept form given the slope and one or
two points, and to write an equation of a line
that is parallel or perpendicular to the graph of a
given equation.
Drill #22*
Write the equation of the line (in point- slope
form) passing through the following points
and graph the line:

1.   ( 2, 5 ) , ( 3, 8 )

2.   ( -1, 3) , ( 2, 4 )

3.   ( 0, 1 ) , ( 3, 1 )
Quiz tomorrow
• Writing equations in point- slope and slope-
intercept forms given a point and the slope
(parallel or perpendicular to another line)
• Graphing linear equations
- know how to use slope and a point to graph
- know how to use two points to graph
• Finding the line of best fit
• Using the line of best fit to make predictions
Classwork (#22*)
4. Find the equation of the line parallel to
y = ¾ x + 2 and passing through ( -2, -4)
and graph the line.
Find the value of k (#22*)
Find the value of k in the following equations
if the given ordered pair is a solution:

5.   5x + ky = 8     (3, -1)

6.   3x + 8y = k     ( 0, ½ )
2-5 Scatter Plots
Objective: To draw scatter plots and to find
and use prediction equations.
Scatter Plot **(25.)
Definition: The graph of related data points
showing the correlation among the points.

• Generally a line of best fit can be drawn that
approximates the relationship between the
points.
• Using the equation of the line of best fit, we
can predict values.
Plot the following data

Note: When scaling axes
find the maximum and
minimum value for each
variable. Make sure
bigger than your
maximum values and
slightly smaller than your
minimum values
Scatter Plot: Weak Positive Correlation
Line of Best-Fit ** (26.)
• The Best-Fit line is
the line that passes
close to most of the
data points. It does
not have to pass
through any of the
data points. You can
use the best-fit line to
make predictions
Equation of the line of best-fit
• Find two points on the
line: (7, 6) and (1, 0)
• Find the slope: 6  0
m=1                7 1
• Substitute m and find b:
y = 1x + b
• Substitute (1, 0) or (7, 6)
0 = 1(1) + b
-1 = b
• y = 1x - 1
Prediction Equation **(27.)
Definition: The prediction equation can be
found using two points from the line of
best fit (they do not have to be data points)

The prediction equation can be used to
estimate the value of one of the variables
given the other.
Slope…
What does the slope mean? What are the
units?

The slope means that the _____________ is
y - unit
_____________ by _____________
inc. / dec.            slope
every ______________
x - unit
Example 2
1. Make a scatter plot of the following data.
2. Draw a line of best fit.
3. Write an equation for the line of best fit relating
the rate of pay (y) to the years of experience
(x)

Exp    9     4     3     1     10    6      12    8

Rate   \$17 \$10 \$10 \$7          \$6    \$12 \$20 \$15

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