$\sum \sqrt{\binom{ab+2c^{2}}{1+ab-c^{2}}} =\binom{ab+2c^{2}}{\sqrt{1+ab-c^{2}}\sqrt{ab+2c^{2}}} \geq \binom{2(ab+2c^{2})}{1+ab - c^{2} +ab + 2c^{2}} \geq \binom{2ab+4c^{2}}{2(a^{2}+b^{2}+ c^{2})}= ab +2c^{2} \rightarrow tt \rightarrow dpcm$
- Lao Hac yêu thích