2

Today: Warm-Up Intro. to

Parallel/Perpendicular Lines Class Work

Parallel lines have the same slopes so find the slope of the given line and the slope you want for a parallel line will be the same.

Perpendicular lines have negative reciprocal slopes. Take the slope of the given line, switch the numerator and denominator and change the sign for the slope of its perpendicular line.

3

1m

3

1m

3

1m

31

3m

Parallel & Perpendicular Lines:

Practice Problems:

EXAMPLE 2

Determine whether lines are parallel or perpendicular

Line a: y = 5x – 3

Line b: x + 5y = 2

Line c: –10y – 2x = 0

SOLUTION Find the slopes of the lines.

Line a: The equation is in slope-intercept form. The slope is 5. Write the equations for lines b and c in slope-intercept form.

EXAMPLE 2:

Line b:x + 5y = 2 5y = – x + 2

Line c: –10y – 2x = 0 –10y = 2x y = – x15

Determine whether lines are parallel or perpendicular

xy = 25

15 +–

Determine which lines, if any, are parallel or perpendicular.

Line a: 2x + 6y = –3

Line b: y = 3x – 8

Line c: –1.5y + 4.5x = 6

ANSWER

parallel: b and c; perpendicular: a and b, a and c

Class Work:

3.1Front is review of Coordinate Plane

UnitReverse is parallel & perpendicular

lines