Smith, David Eugene, 1860-1944 · Boston, New York [etc.] Ginn and Company · leaf 330
yequal to (1) the sum of theangles in sv or (sx — 2)180°, plus (2) the sum of theangles on the other sideofs1,or(51-2)180°,plus (3) the sum of the angles about the various points shown asinside of sp of which there are v — sx points, about each of whichthe sum of the angles is 360°, making (v — sx)… … 320 THE TEACHING OF GEOMETRY This proof is too abstract for most pupils in the highschool, but it is more scientific than those found in anyof the elementary textbooks, and teachers will find it ofservice in relieving their own minds of any question asto the legitimacy of the theorem. Although this…
Geometry
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