a(b+c)/bc+b(a+c)/ac+c(a+b)/ab
=-a^2/bc-b^2/ac-c^2/ab
=(-a^3-b^3-c^3)/abc
a^3+b^3=(a+b)(a^2-ab+b^2)
=-c(a^2-ab+b^2)
=-c[(a+b)^2-3ab]
=-c^3+3abc
a^3+b^3+c^3=3abc
原式=-3
a(b+c)/bc+b(a+c)/ac+c(a+b)/ab
=-a^2/bc-b^2/ac-c^2/ab
=(-a^3-b^3-c^3)/abc
a^3+b^3=(a+b)(a^2-ab+b^2)
=-c(a^2-ab+b^2)
=-c[(a+b)^2-3ab]
=-c^3+3abc
a^3+b^3+c^3=3abc
原式=-3