[Erken]

ถ้า $a,b,c > 0$ จงพิสูจน์ว่า $$
\frac {2a^{2} - bc}{b^{2} - bc + c^{2}} + \frac {2b^{2} - ca}{c^{2} - ca + a^{2}} + \frac {2c^{2} - ab}{a^{2} - ab + b^{2}}\ge 3$$