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2 4 Writing Expressionsof Lines (Day 1 )
Objective CA Standard 1 Students solve
equations and inequalities involving absolute
value.
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Writing Linear Equations
Slope - Intercept Form Given the slope m and
the y-intercept b, use this equation
Point Slope Form Given the slope m and a point
(x1, y1), use this equation
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Two Points Given two point (x1, y1), and (x2,
y2), use the formula
to find the slope m.
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Example 1 Writing an Equation Given the slope
and y-intercept.
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From the graph of the line determine the slope. m
3/2
What is the y-intercept?
(0, -1)
What is an equation of this line?
y mx b
y 3/2 x 1
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Example 2
Write an equation of the line that passes through
(2, 3) and has a slope of ½ .
Use the point slope form
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Example 3
Write an equation of a line that passes through
(3, 2) and is parallel to the line y -3x 2.
If two lines are parallel they have the same
slope. Let m -3 and (x1, y1) (3, -2)
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Use the point slope form.
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Example 4
Write an equation of a line that passes through
(3, 2) and is perpendicular to the line y -3x
2.
If two lines are perpendicular then the product
of their slopes is 1.
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Let m1 -3 m1? m 2 -1 -3 ? m2 - 1 m2
-1/-3 m2 1/3
Use the point slope form find the equation of the
line
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Example 5
Write an equation of a line that passes through
(-2, -1) and (3, 4)
Find the slope
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Use the point slope form.
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Example 6 Writing and using a Linear Model.
In 1984 Americans purchased an average of 113
meals or snacks per person at restaurants. By
1996 this number was 131. Write a linear model
for the number of meals or snacks purchased per
person annually. Then use the model to predict
the number of meals that will be purchased per
person in 2006.
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Average rate of change
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Verbal Model
Labels
Number of Meal y Number in 1984 113 Average
Rate of change 1.5 Year since 1984 t 2006
1984 t 22
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Algebraic Model
y 113 1.5 t y 113 1.5 (22) y 113
33 y 146
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Home work
page 95 14 42 even, and 61
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