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and are separational from a third Line, are coincidental with each other. or, If there be given a Line and a point without it, only one Line can be drawn, through the given point, separational from the given Line. (c) A Pair of Lines, which have a separate point and are separational from a third Line, are separational from each other. [I. 30.] |
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∗16. (a) A Pair of intersectional Lines cannot both be separational from the same Line. (b) A Line, which is intersectional with one of two separational Lines, is intersectional with the other also. |
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∗17. A Line cannot recede from and then approach another; nor can one approach and then recede from another while on the same side of it. |
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18. (a) If a side of a Triangle be produced, the exterior angle is equal to each of the interior opposite angles. [I. 32.] (b) The angles of a Triangle are together equal to two right angles. [I. 32.] |
You will find it convenient to have the Propositions, that have been proposed as Axioms, repeated in a Table by themselves.
