Download - Unit 2.2
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Unit 2.2
Linear Representation and Equations of Lines
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Linear Representations
Linear Data can be represented in a variety of ways:• x-y tables• Graphs• Equations• Verbal representation
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Slope-Intercept Form of a Line
y = mx + b
Slope of line Y-intercept of line
x and y are points (x,y) on the line
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Practice Problems
Identify the slope (m) and y-intercept (b) of the following lines:
1.y = ½ x – 4 2.y = -3x + 53.y = 6 – 2x4.y = -2/3x + 105. y = -8 + .5x
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Writing Linear Equation from Slope and y-intercept
• If we know the slope (m) and y-intercept (b), we can write the equation of a line.
Examples: m = ¾ , b=-6 Equation: y = ¾ x – 6 m = -2, b = 3 Equation: y = -2x + 3 m = 0, b = 5 Equation: y = (0)x + 5 or y = 5
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Practice Problems
• Write the equations for the following lines:
1. m = 3, b = -42. m = -1/2, b=23. m = 6, b = 04. m = 2/5, b = -25. m = 9/5, b = 32
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Write the equation of the line in slope-intercept form for the following graph:
m = b = Equation:
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Writing Equation from the slope and one point
If we know the slope of a line and one point on the line, we can find the y-intercept by doing the following:
1. Replace m with the slope given in the problem2. Use the point we know to replace x and y3. Solve for b
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Example 1:
• Find the equation of the line with a slope of 2 that passes through point (1, 6).
• m = 2, x = 1, y = 6
Use the general equation: y = mx + b to find b 6 = 2(1) + b 6 = 2 + b 4 = b Equation of line: y = 2x + 4
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Example 2:
• Find the equation of the line with a slope of ½ that passes through (4, 8).
m = ½ , x = 4, y = 8y = mx + b8 = ½(4) + b8 = 2 + b6 = b Equation of line: y = ½ x + 6
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Practice Problems
• Write the equation of the line with the following information:
1. m = -3, contains (1, -12)2. m = 4, contains (-1, 6)3. m = -1, contains (0, 3)4. m = 2/3, contains (6, 9)
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Writing Equation from Two Points• We can also write the equation if we know
two points on the line:1. Find the slope of the line passing through the
two points (this is m)2. Find the y-intercept by solving for b using the
slope and one point on the line3. Put m and b into the general equation y = mx + b
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Example:• Find the equation of the line passing through (1,4)
and (2,2).1. Find slope: m = = -2
2. Find b: y = mx + b m = -2, x = 1, y = 4 y = mx + b 4 = -2(1) + b 4 = -2 + b 6 = b 3. Equation: y = -2x + 6
12
42
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Practice Problem
• Find the equation of the line passing through (-2,5) and ( 1,2)
m =
b =
Equation:
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Example 1: Joe puts $50 in a savings account and saves $15 a week.
Table Equation GraphWeek Money
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Example 2: Cost of fixing a furnace Table: Equation: Graph:Hours Cost 0 $50 1 $75 2 $100 3 $125 4 $150
Verbal:
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Example 3: Table EquationX | Y
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Standard Form of a Line
• The standard form of a line is ax + by = cwhere a, b, are integers, c is real number and x and y are points on the line
• The standard form of a line is often used to find x- and y-intercepts.