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sinc cosa+ sinc cosb= cosc sina +cosc sinb,sinc cosa- cosc sina= cosc sinb- sinc cosb,sin(c-a)=sin(b-c),ËùÒÔc-a=b-c,a+b=2c,ÓÖÒòa+b+c=180...


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cos2A=cosA2-sinA2=1-2sinA2=2cosA2-1 tan2A=2tanA/(1-tanA2)=2cotA/(cotA2-1)4¡¢°ë½Ç¹«Ê½ tan(A/2)=(1-cosA)/sinA=sinA/(1+cosA); cot(A/2)=sinA/(1-cosA...


¡÷ABCÖÐ,ÒÑÖªsinB(tanA+tanC)=tanAtanCÇóÖ¤a,b,c³ÉµÈ±È...

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