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余弦定理:a2=b2+c2-2bcosAb2=a2+c2-2acosBc2=a2+b2-2abcosC正弦定理:asinA=sinbB=sincC=2R把正弦定理变形为:a=2RsinA,b=2RsinB,c=2RsinC回代余弦定理并整理可得形似余弦定理的一组公式:sin2A=sin2B+sin2C-2sinBsinCcosAsin2B=sin2A+sin2C-2sinAsinCcosBsin2C=sin2A+sin2B-2si
Cosine Theorem: a2=b2+c2-2bcosAb2=a2+c2-2acosBc2=a2+b2-2abcosC sine theorem: asinA=sinbB=sincC=2R Deform the sine theorem to: a=2RsinA,b=2RsinB,c=2RsinC The cosine theorem and a set of formulas available for the shape of the cosine theorem: sin2A=sin2B+sin2C-2sinBsinCcosAsin2B=sin2A+sin2C-2sinAsinCcosBsin2C=sin2A+sin2B-2si