Parallel and Perpendicular Lines

Warm Up

Find the slope of the lines described (you may
want to plot them on your whiteboard):

1) Line AB with points A(2, 3) and B(7, 6)

2) Line CD with points C(-1, 4) and D(1, 0)

Parallel and Perpendicular

Slopes

I can find the equation of parallel and perpendicular

lines

Parallel Lines

Parallel lines have
equal slopes

The slope of both lines
at the right is 2/6 or
reduced ⅓
(rise 1, run 3)

Perpendicular Lines

Perpendicular
lines have opposite
reciprocal slopes

The slopes of the lines
at the right are 3/4
and -4/3
(one negative, one
positive, and fraction
flipped

Find the slope in the equation

In slope-intercept form:
y = mx + b, m is the slope

y = 2x + 3, 2 is the slope

What is the equation of a line parallel to
y=2x+3? Perpendicular to that line?

Turn standard form into
slope-intercept form

If 3x - 2y = 8, then y = (3/2)x - 4
So, slope is 3/2, parallel slope is 3/2,
perpendicular slope is -2/3

Rearrange the equation by
1. subtracting the x-term from both sides then
2. dividing by the coefficient on y (the number

times y)

Practice at your table

Do odds or evens depending on what you are
assigned on the handout

Add the following directions to your handout:
● Find the slope of the line,
● write the equation of a line parallel to that

line, and

● write the equation of a line perpendicular to

that line.