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2.5.2 – Writing Equations of Lines Cont’d

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Yesterday, we could write equations of lines in a few ways 1) Given slope and y-intercept (y = mx + b) 2) Given a graph of a line, determine slope and y-intercept (also write in y = mx + b) 3) Use point-slope form given any point and slope of a line (y - y 1 = m(x - x 1 )) – Could write in y = mx + b as well if we simplified it

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We’ll start off still using point-slope form, but this time in a different scenario Remember, only need 2 points to represent a line Now, you will be given two points, and you will need to find an equation of that line

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2 points Using two points, we will; 1) Find the slope, using the slope formula; m = 2) Using any of the two points, write in point- slope form 3) Simplify as y = mx + b

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Example. Write an equation of the line that passes through the points (-2, 3) and (2, -5). Slope = m = Point-Slope form; Slope-Intercept form;

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Example. Write an equation of the line that passes through the points (-8, 10) and (-2, 17). Slope = m = Point-Slope form; Slope-Intercept form;

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Graphically Similar to yesterday, you can determine the equation of a line graphically, even if we cannot accurately locate the y-intercept Just find two known points, then 1) Find the slope using rise/run (counting) 2) Pick one point, use point-slope formula

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Example. Write an equation of the line shown.

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Parallel/Perpendicular Equations Recall, we covered parallel and perpendicular lines What determines if two lines are parallel? What determines if two lines are perpendicular? Using given info, we will once again use point- slope form after finding each slope

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Example. Write an equation of the line that is parallel to y = 4x – 5 and goes through the point (-1, 3).

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Example. Write an equation of the line that is perpendicular to y = 4x – 5 and goes through the point (-1, 3).

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Assignment Pg. 98 24, 34-52 even, 59, 60 Pg. 100 11-13

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