4-7A Parallel Lines Algebra 1 Glencoe McGraw-Hill Linda Stamper

Any two horizontal lines are parallel Parallel lines are different lines in the same plane that never intersect. x y Any two horizontal lines are parallel

Any two vertical lines are parallel Parallel lines are different lines in the same plane that never intersect. y x Any two vertical lines are parallel

Two non-vertical lines are parallel if they have the same slope and different y-intercepts. • x • y

Prove whether the graphs of two equations are parallel lines Prove whether the graphs of two equations are parallel lines. Explain your answer. Find two points on each line to determine slope. y • • • x • • • Locate the y-intercepts for each line. a b Line a and line b are parallel because they have the same slope but different y-intercepts.

What about equations that have the same slope and the same y-intercept? x They are the same line.

Write the slope-intercept form of an equation for the line that passes through (3,-2) and is parallel to the graph of y = -2x + 7 Starting with point-slope form. Starting with slope-intercept form.

The equation of this line is Example 1 Write in slope-intercept form the equation of the line that is parallel to the line in the graph and passes through the given point. y • (1,2) • | – x • The equation of this line is y = −3x + 5 What is the equation of the purple line?

Example 2 Write in slope-intercept form the equation of the line that is parallel to the line y = –3x – 2 and passes through the point (3,–4). | –

White Board Practice

Write in slope-intercept form, the equation of the line that is parallel to the given line and passes through the given point. 1) y = 3x − 5; (−5, −2) 2) y = −4x + 1; (2, −1)

Write in slope-intercept form, the equation of the line that is parallel to the given line and passes through the given point. 3) y = −x + 1; (0,−8) 4) y = −5x + 2; (2, 4)

Horizontal line – slope is 0. Write in slope-intercept form, the equation of the line that is parallel to the given line and passes through the given point. 5) y = -7x – 10; (12,2) 6) (−6,−2), y = -4 Horizontal line – slope is 0.

Write in slope-intercept form, the equation of the line that is parallel to the given line and passes through the given point. 7) 8)

Homework 4-A14 Page 240 #10–15 and Skills Practice Wkbk. Page 30 #1-12.