# Lesson 5.5 OBJ: To write equations of parallel and perpendicular lines.

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Lesson 5.5 OBJ: To write equations of parallel and perpendicular lines.

Parallel Lines If two non-vertical lines in the same plane have the same slope, then they are parallel. If two non-vertical lines in the same plane are parallel, then they have the same slope.

Example Write an equation of the lines that passes through point (-2, 11) and is parallel to the line y = -x + 5. Identify the slope. Find the y-intercept. Write the equation in slope-intercept form.

Example Write an equation of the line that passes through (-3, 3) and is parallel to the line y = -2x + 1 You may also use the point slope form of the equation.

Perpendicular Lines Two lines in the same plane that intersect to form a right angle. If two non-vertical lines in the same plane have slopes that are negative reciprocals, then the lines are perpendicular. If two non-vertical lines in the same plane are perpendicular, then their slopes are negative reciprocals.

Examples Write an equation of the line that passes through (4, 3) and is perpendicular to the line y = 4x – 7. Write an equation of the line that passes through (4, -2) and is perpendicular to the line y = 4x +2.

Determine which lines, if any, are parallel or perpendicular. Line a: 2x + 6y = -3 Line b: y = 3x – 8 Line c: -1.5y + 4.5x = 6

Homework Text p. 322-323, #’s 1, 2, 4-26 evens, 28, 29

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