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Parallel, Perpendicular, Coinciding, or Intersecting Lines To determine if the graphs of two equations are lines that are parallel, perpendicular, coinciding, or intersecting (but not perpendicular), put the equations in slope-intercept form (solve each equation for y). Then by looking at the equation you will be able to determine what type of lines they are. Slope-intercept Form y = mx + b m Æ slope b Æ y-intercept Parallel Lines lie in same plane and never intersect have same slope equations have same x-coefficient 1 y = − x −1 2 1 y = − x +2 2 Perpendicular Lines lie in same plane and intersect at 90o angle slopes are negative reciprocals y = 2x − 1 m1 = 2 1 y = − x +2 2 m2 = − 1 2 © LaurusSoft, Inc. Coinciding Lines lie right on top of each other same slope same y-intercept 1 y = − x+2 2 1 y = − x+2 2 Intersect at one point Different slopes Not perpendicular Intersecting Lines 1 y = − x+2 2 y = x −3 © LaurusSoft, Inc.