判断三角形形状(4)acosB + bcosC + ccosA = bcosA + ccosB + acosC.判断三角形形状(4)acosB + bcosC + ccosA = bcosA + ccosB +
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![判断三角形形状(4)acosB + bcosC + ccosA = bcosA + ccosB + acosC.判断三角形形状(4)acosB + bcosC + ccosA = bcosA + ccosB +](/uploads/image/z/6991866-18-6.jpg?t=%E5%88%A4%E6%96%AD%E4%B8%89%E8%A7%92%E5%BD%A2%E5%BD%A2%E7%8A%B6%EF%BC%884%EF%BC%89acosB+%2B+bcosC+%2B+ccosA+%3D+bcosA+%2B+ccosB+%2B+acosC.%E5%88%A4%E6%96%AD%E4%B8%89%E8%A7%92%E5%BD%A2%E5%BD%A2%E7%8A%B6%EF%BC%884%EF%BC%89acosB+%2B+bcosC+%2B+ccosA+%3D+bcosA+%2B+ccosB+%2B)
判断三角形形状(4)acosB + bcosC + ccosA = bcosA + ccosB + acosC.判断三角形形状(4)acosB + bcosC + ccosA = bcosA + ccosB +
判断三角形形状(4)acosB + bcosC + ccosA = bcosA + ccosB + acosC.
判断三角形形状(4)acosB + bcosC + ccosA = bcosA + ccosB +
判断三角形形状(4)acosB + bcosC + ccosA = bcosA + ccosB + acosC.判断三角形形状(4)acosB + bcosC + ccosA = bcosA + ccosB +
设a/sinA=b/sinB=c/sinC=k,则a=ksinA,b=ksinB,c=ksinc acosB+bcosC+ccosA=bcosA+ccosB+acosC ksinAcosB+ksinBcosC+ksinCcosA=ksinBcosA+ksinCcosB+ksinAcosC sinAcosB+sinBcosC+sinCcosA=sinBcosA+sinCcosB+sinAcosC (两边同除k) sinAcosB-sinBcosA+sinBcosC-sinCcosB+sinCcosA-sinAcosC=0 (移项) sin(A-B)+sin(B-C)+sin(C-A)=0 (正弦差公式的逆向应用) 当sin(A-B),sin(B-C),sin(C-A)等于0时,等式成立,此时,A-B=0,B-C=0,C-A=0 所以A=B=C,所以三角形为等边三角形
sinAcosB+sinBcosC+sinCcosA=sinBcosA+cosCsinB+sinAcosC sin(A-B)+sin(B-C)+sin(B-C)=0 A=B=C 等边三角形