Page:First six books of the elements of Euclid 1847 Byrne.djvu/22

xviii THE ELEMENTS OF EUCLID.

BOOK I.

DEFINITIONS.

I.

A point is that which has no parts.

II.

A line is length without breadth.

III.

The extremities of a line are points.

IV.

A straight or right line is that which lies evenly between its extremities.

V.

A surface is that which has length and breadth only.

VI.

The extremities of a surface are lines.

VII.

A plane surface is that which lies evenly between its extremities.

VIII.

A plane angle is the inclination of two lines to one another, in a plane, which meet together, but are not in the same direction.

IX.

A plane rectilinear angle is the inclination of two straight lines to one another, which meet together, but are not in the same straight line.

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