Smith, David Eugene, 1860-1944 · Boston, New York [etc.] Ginn and Company · leaf 221
it is perpendicular to thevertical line BC. Thus, ifa class wishes to deter-mine the horizontal lineAC, while sighting up ahill in the direction AB,this is easily determinedwithout a spirit level. It follows from this corollary, as the pupil has alreadyfound, that the mid-point of the hypotenuse of…
Geometry
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