Smith, David Eugene, 1860-1944 · Boston, New York [etc.] Ginn and Company · leaf 278
hould be observed that a2 = //-+ c2-2bc.If ZA = 90 . then &=0, and thisbecomes - = -+<-■ a r b It /. A is obtuse, then // passes through 0 and becomes nega-tive, and <r= b2 -f ca + 2 AV. Thus we have three propositions in one. At the close of Book IV many geometries give asan exercise,… … A rea = Vs ([g —a ) (s — !>) (s — e), where a, 6, and c are tland s is the semipereter^(a + J + <?). As;practical ap-plication the(dass may beable to find a triangular piece of land, as here shown, and to meas-ure the sides. It* the piece is (dear, the result may bechecked by measuring the…
Geometry
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