Wentworth, G. A. (George Albert), 1835-1906 · Boston, Ginn & company · leaf 55
a2 = h2 + BD-BD = c — AD.BD = AD — c;BD2 = AD2 -2cxAD + c2. h2 + AD2 + c2-2cxAD. h2 + AD2 = b2, In Tigs. 56 and 57,In Fig. 56,In Fig. 51,In either case,Therefore, in all cases,Now,and AD = b cos A. Therefore, a2 = b2 + c2 - 2 be cos A. [26~\ In like manner it may be proved that b2 = a2 + c2 — 2 ac…
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