 Parallel Lines = Lines in the same plane that never intersect.  Review:  Slope-Intercept form: y = mx+b

 Write an equation in slope-intercept form for both of the lines below….what do you notice? y = ⅔x + 5 y = ⅔x - 3

 Parallel Lines have the SAME slope and DIFFERENT y-intercepts.  To determine whether lines are parallel, you just compare the slopes and the y-intercepts…  If slopes are the same and different y-intercepts – the lines are parallel  If slopes are the same and the same y-intercepts - you have the same line  If slopes are different – the lines are not parallel

1. y = - ⅓x + 5 and 2x + 6y = x + 8y = -24 and y = ¾x - 7

3x + 4y = 12 and y = ½x + 5

1. Identify the slope of the given line 2. Write an equation in Point-Slope form using the identified slope and the given point. y – y 1 = m(x – x 1 ) 3. Convert to Slope-Intercept form (solve for y) y = mx + b

 Write an equation in slope-intercept form for the line that contains (8, 2) and is parallel to y = ⅝x - 4

 Write and equation in slope-intercept form for the line that contains (2, -6) and is parallel to y = 3x + 9

 Perpendicular Lines = Lines that intersect to form right angles (90°)

Write an equation in slope-intercept form for both of the lines below….what do you notice? y = ¾x + 3 y = -(4/3)x + 5

 The slopes of perpendicular lines are negative reciprocals of each other.  Negative reciprocals:  Ex. The negative reciprocal of ½ is -2. The negative reciprocal of -¾ is 4/3.

 What is the slope of a line perpendicular to… y = ⅝x + 5 6x + 8y = 24

 Are each pair of lines parallel, perpendicular, or neither? y = 3x – 8 and 3x – y = -1

 Are each pair of lines parallel, perpendicular, or neither? 9x + 3y = 6 and 3x + 9y = 6

 Are each pair of lines parallel, perpendicular, or neither? y = -(5/2)x + 11 and -5x + 2y = 20

 Write an equation in slope-intercept form of the line that contains (1, 8) and is perpendicular to y = ¾x + 1.