∵1/a^3+1/b^3+1/c^3≥3*3次√[1/(a^3b^3c^3)]
∴1/a^3+1/b^3+1/c^3≥3/abc
又∵ 1/a^3+1/b^3+1/c^3+abc≥2√(3/abc*abc)=2√3