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AMSCO'S Geometry. New York - Rye High School

AMSCO'S Geometry. New York - Rye High School

AMSCO'S Geometry. New York - Rye High School

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The Slopes of Perpendicular Lines 309Theorem 8.3bIf the slopes of two lines are negative reciprocals, then the two lines areperpendicular.Given Two lines, AB gand AC g, that intersect atA. The slope of AB g is m and the slopeof AC gis 2m1 , the negative reciprocalof m.Prove AB g ' AC gyOBACDxProof Statements Reasons1. AC gis not perpendicular 1. Assumption.to AB g.2. Construct AD gperpendicular 2. At a point on a given line, one andto AB gat A. only one perpendicular can bedrawn.3. Slope of AB gis m. 3. Given.4. The slope of AD gis 2m1 . 4. If two lines are perpendicular, theslope of one is the negative reciprocalof the slope of the other.5. The slope of AC gis 2m1 . 5. Given.6. A, C, and D are on the same 6. Three points lie on the same line ifline, that is, AC gand AD gare and only if the slope of thethe same line.segment joining two of the pointsis equal to the slope of a segmentjoining another pair of thesepoints.7. AC g ' AB g7. Contradiction (steps 1, 6).

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