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Slopes of Parallel and Perpendicular Lines. 4-9. Holt Algebra 1. Warm Up. Lesson Presentation. Lesson Quiz. Holt McDougal Algebra 1. Essential Objectives. Identify and graph parallel and perpendicular lines. Write equations to describe lines parallel or perpendicular to a given line.

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4-9

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  1. Slopes of Parallel and Perpendicular Lines 4-9 Holt Algebra 1 Warm Up Lesson Presentation Lesson Quiz Holt McDougal Algebra 1

  2. Essential Objectives Identify and graph parallel and perpendicular lines. Write equations to describe lines parallel or perpendicular to a given line.

  3. Vocabulary parallel lines perpendicular lines

  4. Parallel linesare lines in the same plane that have no points in common. In other words, they do not intersect.

  5. 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. Example: Identifying Parallel Lines

  6. y = 2x – 3 slope-intercept form slope-intercept form   Example : Identifying Parallel Lines y = 3x – 10

  7. y = 3x   Check It Out! Identify which lines are parallel.   y = 3x + 7

  8. Perpendicular lines are lines that intersect to form right angles (90°).

  9. y = 3; x = –2; y = 3x; . Example 3: Identifying Perpendicular Lines y = 3 andx = –2; y = 3x and

  10. y = 3 x = –2 y =3x Continued

  11. 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 = 3x + 8. Step 1 Find the slope of the line. The slope is 3. y = 3x + 8 Step 2 Write the equation in point-slope form. y – y1 = m(x – x1) y – 10 = 3x – 12 y – 10 = 3(x – 4) y = 3x – 2

  12. 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 = 4x + 5

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