« ΠροηγούμενηΣυνέχεια »
I. A POINT is that which has no parts, or which has no magnitude.
A line is length without breadth.
The extremities of a line are points.
4. A straight line is that which lies evenly between its extreme points.
5. A superficies is that which has length and breadth.
6. A plane superficies is that in which any two points being taken, the straight line between them lies wholly in that superficies.
7. A plane rectilineal angle is the inclination of two straight lines to one another, which meet together, but are not in the same straight line.
12. And this point is called the centre of the circle (C).
13. A radius is a straight line drawn from the centre to the circumference (CD).
14. A diameter is a straight line drawn through the centre, and terminated both ways by the circumference (AB).
15. A semicircle is the figure contained by a diameter and part of the circumference cut off by the diameter (ADB).
16. A triangle is a plane figure contained by three straight lines.
The diagonal of a trapezium is the straight line
which joins two opposite angles (AC).
23. Parallel straight lines are such as are in the same plane and being produced ever so far both ways do not meet.