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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
          your axes are slightly
          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
               about the data.
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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posted:8/31/2012
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