13. Two straight lines cannot enclose a space.
Problems in Geometrical Drawing.
Fig. 99.
Example 1.—To bisect (cut in two) a straight line or an arc of a circle, [Fig. 99]. From the ends of A B as centers, describe arcs cutting each other at C and D, and draw C D, which cuts the line at E or the arc at F.
Ex. 2.—To draw a perpendicular to a straight line, or a radial line to a circular arc, [Fig. 99]. Operate as in the foregoing problem. The line C D is perpendicular to A B; the line C D is also radial to the arc A B.
Fig. 100.
Fig. 101.