# 3.8 Slopes of Parallel and Perpendicular Lines

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3.8 Slopes of Parallel and Perpendicular Lines
Slopes of Parallel Lines If two nonvertical lines are parallel, then their slopes are equal. If the slopes of two distinct nonvertical lines are equal, then the lines are parallel. Any two vertical lines or horizontal lines are parallel.

Checking for Parallel Lines
Are lines ℓ1 and ℓ2 parallel? Explain.

Checking for Parallel Lines
Find the slope of each line. NOT PARALLEL!!!!!!

Writing Equations of Parallel Lines
What is an equation of the line parallel to y = -3x – 5 that contains (-1 , 8)? y = -3x – 5 parallel slope = -3 y – y1 = m (x – x1) y – 8 = -3 (x + 1)

Slopes of Perpendicular Lines
If two nonvertical lines are perpendicular, then the product of their slopes is -1 (opposite reciprocal). If the slopes of two lines have a product of -1, then the lines are perpendicular. Any horizontal line and vertical line are perpendicular.

Checking for Perpendicular Lines
Lines ℓ1 and ℓ2 are neither horizontal nor vertical. Are they perpendicular? Explain.

Checking for Perpendicular Lines
Find the slope of each line. Perpendicular. The slopes have a product of -1.

Writing Equations of Perpendicular Lines
What is an equation of the line perpendicular to that contains (15 , -4)?

More Practice!!!!! Homework – Textbook p. 201 – 202 #8 – 20 even.