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The Law of Cosines February 25, 2010 Solving Oblique Triangles Solving a triangle means finding the lengths of all the sides and the measures of all the angles. This problem requires that we know three of the sides or angles. The Law of Sines We use the Law of Sines if we know: • Two angles and any side (AAS or ASA) • One angle and two sides, where one of the sides is opposite the known angle (SSA) Law of Cosines We use the Law of Cosines if we know: • One angle and its two adjacent sides (SAS) • All three sides (SSS) Questions • What about AAA? • On page 612, why are there “Alternative Forms” of the Law of Cosines? • Do we really need three equations for the Law of Cosines? Homework Page 617, 1 – 7 (odd)