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Linear Equations By Matty Lu and Mc-Welch

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Basics Slope-Intercept Form y = mx + b m = slope b = y-intercept Ex. y = 2/3x + 2 slope = 2/3 y-intercept = 2

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Slope y = mx + b slope= rise/run slope = y = y2-y1 x x2-x1 Ex. (-3,0) (3,4) slope= = 2 3-(-3) 3

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y-intercept y = mx + b b = x-value at which line crosses y-axis 1.Plug in coordinates for x and y 2.Plug in slope for m 3.Solve for b Ex. (3,4) m= 2/3 y = mx + b 4=(2/3)(3) + b 4 = 2 + b 2 = b

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Example 1 Write in slope-intercept form the equation of the line that passes through the given points. Ex. 1. (6,2), (8,-4) Step 1 -4 –2 = Step 2 y = mx + b 2 = (-3)6 + b b = 20 Final Step y = mx + b y = -3x + 20

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Example 2 Using the graph, identify y-intercept and slope and put into slope-intercept form y-intercept = 1 slope = -4 y = -4x + 1

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Example 3 Between , a company’s profits decreased by about $1200 per year. In 1997, the company had an annual profit of $1,500,000. Write an equation that gives the annual profit P in terms of the year t. Let t=0 represent 1995.

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Example 3 (cont.) Step 1: Identify key values x = years (t) y = $profit (P) slope = -$1200/yr point (2, ) with 2 representing the year 1997 Step 2: Substitute values into equation, and solve for b y = mx + b = (-1200)(2) + b b = Step 3: Write equation y = mx + b y = -1200x

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Extra Problems Write equation using the given information. 1.m = 4, b = -2 2.m = -5, b = 3 3.(2, 6), m = 2 4.(3, -9), m = -5 5.(-2, 5), (2, 4) 6.(9, -1), (1, -9) Click for the answers. 1.y = 4x – 2 2.y = -5x y = 2x y = -5x y = -1/4x + 9/2 6.y = x – 10

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Website Links - explanations For additional practice go to the following website,

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