# Slopesofof Paralleland and Perpendicular 4 9 Lines Perpendicular

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Slopesofof. Paralleland and. Perpendicular 4 -9 Lines Perpendicular Lines Warm Up Lesson Presentation Lesson Quiz Holt 1 Algebra Holt. Algebra Mc. Dougal Algebra 11 Mc. Dougal

4 -9 Slopes of Parallel and Perpendicular Lines Essential Objectives Identify and graph parallel and perpendicular lines. Write equations to describe lines parallel or perpendicular to a given line. Holt Mc. Dougal Algebra 1

4 -9 Slopes of Parallel and Perpendicular Lines Vocabulary parallel lines perpendicular lines Holt Mc. Dougal Algebra 1

4 -9 Slopes of Parallel and Perpendicular Lines Parallel lines are lines in the same plane that have no points in common. In other words, they do not intersect. Holt Mc. Dougal Algebra 1

4 -9 Slopes of Parallel and Perpendicular Lines Example: Identifying Parallel Lines The lines described by And both have slope . These lines are parallel. The lines y = x and y = x + 1 both have slope 1. These lines are parallel. Holt Mc. Dougal Algebra 1

4 -9 Slopes of Parallel and Perpendicular Lines Example : Identifying Parallel Lines y = 2 x – 3 slope-intercept form y = 3 x – 10 Holt Mc. Dougal Algebra 1

4 -9 Slopes of Parallel and Perpendicular Lines Check It Out! Identify which lines are parallel. y = 3 x + 7 Holt Mc. Dougal Algebra 1

4 -9 Slopes of Parallel and Perpendicular Lines Perpendicular lines are lines that intersect to form right angles (90°). Holt Mc. Dougal Algebra 1

4 -9 Slopes of Parallel and Perpendicular Lines Example 3: Identifying Perpendicular Lines y = 3; x = – 2; y = 3 x; y = 3 and x = – 2; y = 3 x and Holt Mc. Dougal Algebra 1 .

4 -9 Slopes of Parallel and Perpendicular Lines x = – 2 Continued y =3 x Holt Mc. Dougal Algebra 1 y=3

4 -9 Slopes of Parallel and Perpendicular Lines Example Write an equation in slope-intercept form for the line that passes through (4, 10) and is parallel to the line described by y = 3 x + 8. Step 1 Find the slope of the line. The slope is 3. y = 3 x + 8 Step 2 Write the equation in point-slope form. y – y 1 = m(x – x 1) y – 10 = 3(x – 4) Holt Mc. Dougal Algebra 1 y – 10 = 3 x – 12 y = 3 x – 2

4 -9 Slopes of Parallel and Perpendicular Lines Lesson Quiz: Part I Write an equation is slope-intercept form for the line described. 1. contains the point (8, – 12) and is parallel to 2. contains the point (4, – 3) and is perpendicular to y = 4 x + 5 Holt Mc. Dougal Algebra 1

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