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( 1 )s in s in s in, , , s in s in , s in s in , s in s ins in s in s inA a C c B b a B b A a C c A b C c BB b A a C c? ? ? ? ? ?. ( 2 )s in s in s in s in s in s in s in s in s in s in s in s ina b c a b a c b c a b cA B C A B A C B C A B C? ? ? ? ?? ? ? ? ? ?? ? ? ? ?. ( 3) : : s i n : s i n : s i na b c A B C? . ( 4)正弦定理的推廣: 2si n si n si na b c RA B C? ? ?, 其中