5. Using Parallel and Perpendicular Lines
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Consider the Slopes of Perpendicular Lines Theorem.
Statements
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Reasons
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1. a and b are vertical lines.
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1. Given.
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2. a and b are perpendicular to a horizontal line c.
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2. Slopes of Perpendicular Lines Theorem.
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3. a and b are parallel lines.
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3. Lines Perpendicular to a Transversal Theorem.
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Let a and b be two vertical lines, being cut by a horizontal transversal c. By the Slopes of Perpendicular Lines Theorem, a and b are both perpendicular to c.
By the Lines Perpendicular to a Transversal Theorem, we have that a and b are parallel lines.
Lines Perpendicular to a Transversal Theorem a∥ b We can summarize our proof in a two-column proof table.
Statements
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Reasons
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1. a and b are vertical lines.
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1. Given.
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2. a and b are perpendicular to a horizontal line c.
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2. Slopes of Perpendicular Lines Theorem.
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3. a and b are parallel lines.
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3. Lines Perpendicular to a Transversal Theorem.
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