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(d)/(dx)(a^x/(b^x+c^x)+b^x/(a^x+c^x)+c^x/(b^x+a^x)) = (a^x log(a))/(b^x+c^x)-(a^x (b^x log(b)+c^x log(c)))/(b^x+c^x)^2+(b^x log(b))/(a^x+c^x)-(c^x (a^x log(a)+b^x log(b)))/(a^x+b^x)^2+(c^x log(c))/(a^x+b^x)-(b^x (a^x log(a)+c^x log(c)))/(a^x+c^x)^2
假设a＞b＞c合并同类项log(a/b) log(a/c) log(b/c)即可知x＞0时，d/dx＞0。x＜0时,d/dx＜0
假设a＞b＞c合并同类项log(a/b) log(a/c) log(b/c)即可知x＞0时，d/dx＞0。x＜0时,d/dx＜0
