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1 
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Nonadjacent interior angles that lie on opposite sides of the transversal 
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2 
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Two angles whose sides are opposite rays 
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3 
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An 'if-then' statement 
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4 
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Axiom; an accepted statement of fact 
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5 
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A part of a line that consists of two endpoints and all points between 
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6 
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The process of making conjectures based on patterns 
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7 
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An angle that is greater than 0 degrees, but less than 90 degrees 
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8 
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Formed by two rays with the same endpoint 
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9 
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An angle that is equal to 180 degrees 
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