\[\begin{array}{rcl}
\frac{a}{b+c}+\frac{b}{c+a}+\frac{c}{a+b}-\frac{9}{6} & \geq & \frac{4}{6}-\frac{2(ab+bc+ca)}{3(a^2+b^2+c^2)} \\
\frac{a}{b+c}+\frac{b}{c+a}+\frac{c}{a+b}-\frac{3}{2} & \geq & \frac{2}{3(a^2+b^2+c^2)}(a^2+b^2+c^2-ab-bc-ca) \\
\frac{(a-b)^2}{2(b+c)(c+a)}+\frac{(b-c)^2}{2(c+a)(a+b)}+\frac{(c-a)^2}{2(a+b)(b+c)} & \geq & \frac{2}{3(a^2+b^2+c^2)}\frac{1}{2}[(a-b)^2+(b-c)^2+(c-a)^2] \\
\sum [\frac{1}{2(b+c)(c+a)}-\frac{1}{3(a^2+b^2+c^2)}](a-b)^2 & \geq & 0 \\
\end{array}\]
สมมติโดยไม่เสียนัย $a\geq b \geq c$ จะได้ว่า $\frac{1}{b+c} \geq \frac{1}{c+a} \geq \frac{1}{a+b}$ และกำหนดให้
\[\begin{array}{cl}
S_{a}& =\frac{1}{2(c+a)(a+b)}-\frac{1}{3(a^2+b^2+c^2)} \\
S_{b}& =\frac{1}{2(a+b)(b+c)}-\frac{1}{3(a^2+b^2+c^2)} \\
S_{c}& =\frac{1}{2(b+c)(c+a)}-\frac{1}{3(a^2+b^2+c^2)} \\
\end{array}\]
\[\begin{array}{cl}
S_{b}& =\frac{1}{2(a+b)(b+c)}-\frac{1}{3(a^2+b^2+c^2)} \\
& =\frac{3a^2+b^2+3c^2-2ab-2bc-2ca}{6(a+b)(b+c)(a^2+b^2+c^2)} \\
& =\frac{c^2+a^2-b^2+(a-b)^2+(b-c)^2+(c-a)^2}{6(a+b)(b+c)(a^3+b^3+c^3)} \\
& \geq 0
\end{array}\]
\[\begin{array}{cl}
S_{c}& =\frac{1}{2(b+c)(c+a)}-\frac{1}{3(a^2+b^2+c^2)} \\
& =\frac{3a^2+3b^2+c^2-2ab-2bc-2ca}{6(a+b)(b+c)(a^2+b^2+c^2)} \\
& =\frac{a^2+b^2-c^2+(a-b)^2+(b-c)^2+(c-a)^2}{6(a+b)(b+c)(a^3+b^3+c^3)} \\
& \geq 0
\end{array}\]
\[\begin{array}{cl}
S_{a}+S_{b}& =\frac{1}{2(a+b)(c+a)}-\frac{1}{3(a^2+b^2+c^2)}+\frac{1}{2(b+c)(a+b)}-\frac{1}{3(a^2+b^2+c^2)} \\
& =\frac{a^2+3b^2+3c^2-2ab-2bc-2ca}{6(c+a)(a+b)(a^2+b^2+c^2)}+\frac{3a^2+b^2+3c^2-2ab-2bc-2ca}{6(a+b)(b+c)(a^2+b^2+c^2)} \\
& =\frac{b^2+c^2-a^2+(a-b)^2+(b-c)^2+(c-a)^2}{6(c+a)(a+b)(a^3+b^3+c^3)}+\frac{c^2+a^2-b^2+(a-b)^2+(b-c)^2+(c-a)^2}{6(a+b)(b+c)(a^3+b^3+c^3)} \\
& \geq \frac{b^2+c^2-a^2+(a-b)^2+(b-c)^2+(c-a)^2}{6(c+a)(a+b)(a^3+b^3+c^3)}+\frac{c^2+a^2-b^2+(a-b)^2+(b-c)^2+(c-a)^2}{6(a+b)(c+a)(a^3+b^3+c^3)} \\
& =\frac{2c^2}{6(a+b)(c+a)(a^3+b^3+c^3)} \\
& \geq 0
\end{array}\]