Wentworth, G. A. (George Albert), 1835-1906 · Boston, Ginn & company · leaf 70
— b + c) 2be 2(s — b)(s-c) be and the value of 1 + cos A is £2 + c2 _ a2 2bc + b2 + C2-C 2 be 1 + (b + ey 2 be 2 be 2 be _ (b + c + a) (b + c — a) _ 2 s (s — a)~ 2 be ~ be THE OBLIQUE TRIANGLE 81 But from Formulas [16] and [17], p. 58, it follows that1 — cos A = 2 sin2 £ A, and 1 + cos A = 2 cos2 £… … sin # c=^«-«)(*-*) cos+c = \fc^ 2 * aft s(s-b) X s(s-c) tan i- There is then a choice of three different formulas for findingthe value of each angle. If half the angle is very near 0°,the formula for the cosine will not give a very accurate result,because the cosines of angles near 0° differ little…
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