R
rua_it
[tex]LHS=\sum \frac{1}{ab+2c^2+2c} =\sum \frac{(ab)^2}{a^2b^2.(ab+2c^2+2c)}[/tex]:-?? Em không hiểu gì cả ạ![]()
[tex]=\sum \frac{(ab)^2}{a^3b^3+2(abc)^2+2a^2b^2c} \geq \frac{(ab+bc+ca)^2}{a^3b^3+2(abc)^2+2a^2b^2c+b^3.c^3+2(abc)^2+2b^2c^2a+c^3a^3+2(abc)^2+2c^2a^2b}[/tex]
[tex]=\frac{(\sum ab)^2}{\sum a^3b^3+2abc.\sum a +6a^2b^2c^2}[/tex]
ok.