$\"\"$

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Observe the figure, The coordinate points are $\"\"$ .

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Let the slope of the line be $\"\"$ .

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Derive the slope $\"\"$ by using the formula $\"\"$ .

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$\"\"$ (Substitute $\"\"$ )

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$\"\"$ (Subtract: $\"\"$ )

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$\"\"$ (Divide: $\"\"$ ) $\"\"$

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If the two nonvertical lines are parallel, then their slopes are equal. That is $\"\"$ .

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Therefore slope of a parallel line $\"\"$ is also $\"\"$ .

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If the two nonvertical lines are perpendicular, then their slopes are negative reciprocals of each other. That is $\"\"$ .

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Therefore slope of perpendicular line is $\"\"$ . $\"\"$

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The slope of a parallel line is $\"\"$ and the slope of a perpendicular line is $\"\"$ .