Writing Equations Given a Point and a Slope

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5.2
Writing Equations Given a Point and a Slope

• Goals
• Write an equation of a line
• Write equations of parallel lines
• Model a real-life situation with a linear equation

• Vocabulary
• Point-slope form of an equation
• Linear modeling

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POINT-SLOPE FORM
The point-slope form of the equation of the line
through (x1 , y1) with slope m is y y1 m(x
x1)

• Point-Slope Form from a Graph

Write the equation of the line in the graph in
point-slope form.
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Write the equation of the line in the graph in
point-slope form.
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Write the equation of the line in the graph in
point-slope form.
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Write the equation of the line in the graph in
point-slope form.
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• Write an Equation in Point-Slope Form

Write in point-slope form the equation of the
line that passes through the point (1, -5) with
slope 3.
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Write in point-slope form the equation of the
line that passes through the point (2,2) with
slope .
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• Use Point-Slope Form

Write in slope-intercept form the equation of the
line that passes through the point (-3, 7) with
slope -2.
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Write in slope-intercept form the equation of the
line that passes through the point (2, 4) with
slope 3. Check your answer by graphing.
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• Write an Equation of a Parallel Line

Write in slope-intercept form the equation of the
line that is parallel to the line y 2x - 3 and
passes through the point (3, -1).
Check your answer graphically.
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Write in slope-intercept form the equation of the
line that is parallel to the line y -2x 1 and
passes through the point (3, -2).
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• Classified Ads
• It costs 2.00 per day to place a one-line ad in
  the classifieds plus a flat service fee. One day
  costs 3.00 and four days costs 9.00.
• Write a linear equation in point-slope form that
  gives the cost in dollars, y, in terms of the
  number of days the ad appears, x.
• Find the cost of a six-day ad.

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SUMMARY

• Writing Equations of Lines
• Use slope-intercept form y mx b if you are
  given the slope m and the y-intercept b.
• Use point-slope form y y1 m(x x1) if you
  are given the slope m and a point (x1, y1)

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Homework pp. 282-4, 12-40 evens, 44, 45, 48-50,
57-8, 71-4