© LaurusSoft, Inc. 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 Perpendicular Lines lie in same plane and intersect at 90o angle slopes are negative reciprocals 21m2m21−==2x21y+−=12xy−=2x21y+−=1x21y−−=
© LaurusSoft, Inc. Coinciding Lines lie right on top of each other same slope same y-intercept Intersecting Lines Intersect at one point Different slopes Not perpendicular 2x21y+−=2x21y+−=2x21y+−=3xy−=