4.3 Parallel vs. Perpendicular Lines

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What is the definition of parallel lines?

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Parallel lines are lines in a plane that never meet. They have the same slope but different y-intercepts.

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What is the definition of perpendicular lines?

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Perpendicular lines are lines that intersect at a right angle (90 degrees). The slopes of perpendicular lines are negative reciprocals of each other.

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What is the slope of a line perpendicular to a line with slope 5?

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If two lines are parallel, what can be said about their slopes?

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If two lines are parallel, their slopes are equal.

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If two lines are perpendicular, how do you find the slope of one line if you know the slope of the other?

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To find the slope of a line perpendicular to another, take the negative reciprocal of the known slope.

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