Smith, David Eugene, 1860-1944 · Boston, New York [etc.] Ginn and Company · leaf 181
ing applied prob-lemx depending upon the theorem given on page 171. Wishing to measure the distanceacross a river, some boys sightedfrom A to a point P. They thenturned and measured AB at rightangles to A P. They placed a stakeat 0, halfway from A to B, anddrew a perpendicular to AB at B.They… … BOOK I AND ITS PROPOSITIONS 171 This involves the ranging of a line, and the runningof a line at right angles to a given line, both of whichhave been described in Chapter IX. It is also fairlyaccurate to run a line at any angle to a given line bysighting along two pins stuck in a protractor.…
Geometry
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