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LESSON 5-8 Perpendicular Slope & Equation of Perpendicular Lines

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Math Vocabulary Perpendicular Lines: two lines on a graph, that DO intersect, forming a right angle, based on opposite slope

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Finding Parallel Slope… Perpendicular Lines have… The opposite/reciprocal slope! If y = 3/5 x – 4 m = 3/5 then perpendicular slope perpendicular m = - 5/3

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Finding Parallel Slope… Find the slope of a line perpendicular to the equation… y = -5 x – 3 m = -5 perpendicular m = 1/5 Find the slope of a line perpendicular to the equation… x – 3y = 7 *Needs to be in y = mx + b x – 3y = 7 -x -x -3y = -x + 7 -3 -3 -3 y = 1/3 x – 7/3 m = 1/3 perpendicular m = - 3

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Finding Perpendicular Slope… Find the slope of a line perpendicular to the equation… y = -4x + 7 m = -4 perpendicular m = ¼ Find the slope of a line perpendicular to the equation… 3y + 6x = 12 *Needs to be in y = mx + b m = -2 perpendicular m = ½

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Equation of a line with Perpendicular Slope… Finding the equation of a line perpendicular to y = -4x + 1 AND… that passes thru the point (-8, 0) 1) Name the current slope m = -4 2) Name the perpendicular slope perpendicular m = 1/4 2) Solve to write the equation with… m = 1/4, thru (-8, 0) y = mx + b 0 = ¼ (-8) + b 0 = -8/4 + b 0 = -2 + b +2 2 = b Eq. y = ¼ x + 2

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Practice… Find the parallel & perpendicular slope of each equation of a line… a) y = - 8/3x + 5parallel m = perp m = b) 15x + 3y = -3parallel m = perp m = c) Write the equation of a line perpendicular to y = -2x + 1, and that passes thru (-4, 3)

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Homework p. 253-254 #13-17, 21-23, 42, 43

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