设ax^3=by^3=cz^3=s^3,∴(ax^2+by^2+cz^2)^1\3=(s^3/x+s^3/y+s^3/z)^1/3=[s^3(1/x+1/y+1/z)]^1/3=s∵a^1\3+b^1\3+c^1\3=s/x+s/y+s/z=s(1/x+1/y+1/z)=s∴(ax^2+by^2+cz^2)^1\3=a^1\3+b^1\3+c^1\3.