Kitap 1
DEFINITIONS.
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1
A point is that which has no part.
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2
A line is breadthless length.
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3
The extremities of a line are points.
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4
A straight line is a line which lies evenly with the points on itself.
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5
A surface is that which has length and breadth only.
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6
The extremities of a surface are lines.
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7
A plane surface is a surface which lies evenly with the straight lines on itself.
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8
A plane angle is the inclination to one another of two lines in a plane which meet one another and do not lie in a straight line.
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9
And when the lines containing the angle are straight, the angle is called rectilineal.
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10
When a straight line set up on a straight line makes the adjacent angles equal to one another, each of the equal angles is right, and the straight line standing on the other is called a perpendicular to that on which it stands.
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11
An obtuse angle is an angle greater than a right angle.
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12
An acute angle is an angle less than a right angle.
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13
A boundary is that which is an extremity of anything.
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14
A figure is that which is contained by any boundary or boundaries.
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