Writing Equations in Slope-Intercept Form

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Lesson 5-4

• Writing Equations in Slope-Intercept Form

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display the answers.
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Objectives

• Write an equation of a line given the slope and
  one point on a line
• Write an equation of a line given two points on a
  line

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Vocabulary

• Linear extrapolation the use of a linear
  equation to predict values that are outside the
  data range

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x-y Coordinate Plane
Quadrants
Point Plotting
I
II
up 7
left 4
right 5
III
IV
down 8
(x, y) (-4, 7) (5, -8) x left or
right y up or down
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Example 1
Write an equation of a line that passes through
(2, 3) with slope ½
Step 1 The line has slope ½ To find the
y-intercept,replace m with ½ and (x, y) with
(2, 3) in theslope-intercept form. Then, solve
for b.
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Example 1 cont
Using your calculator to graph it and the CALC
menu to verify that it passes through (2, 3).
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Example 2
Economy In 2000, the cost of many items
increased because of the increase in the cost of
petroleum. In Chicago, a gallon of self-serve
regular gasoline cost 1.76 in May and 2.13 in
June. Write a linear equation to predict the cost
of gasoline in any month in 2000, using 1 to
represent January.
Explore You know the cost of regular gasoline in
May and June. Plan Let x represent the month and
y represent the cost of gasoline that month.
Write an equation of the line that passes
through (5, 1.76) and(6, 2.13).
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Example 2 cont
Solve Find the slope.
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Example 2 cont
Choose (5, 1.76) and find the y-intercept of the
line.
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Example 3
Answer If gas increases at the same rate, a
gallon of gasoline will cost 2.50 in July. 3000
gallons at this price is 7500, so they will have
to add 500 to their budget.
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Summary Homework

• Summary
• To write an equation given the slope and one
  point, substitute the values of m, x, and y into
  the slope-intercept form and solve for b. Then
  write the slope-intercept form using the values
  of m and b
• To write an equation given two points, find the
  slope. Then follow the steps above
• Homework
• Pg 284 12-32 even