cho $\left\{\begin{matrix} a,b,c >0 & & \\ a+b=c\leq 1& & \end{matrix}\right.$
tìm GTNN
$a, P=\frac{1}{a^{2}}+\frac{1}{b^{2}}+\frac{1}{c^{2}}+\frac{2}{ab}+\frac{2}{ac}+\frac{2}{bc}$
$b, \frac{1}{a^{2}+b^{2}}+\frac{1}{b^{c}+c^{2}}+\frac{1}{a^{2}+c^{2}}+\frac{1}{ab}+\frac{1}{bc}+\frac{1}{ac}$
$c, \frac{1}{a^{2}+bc}+\frac{1}{b^{2}+ac}+\frac{1}{c^{2}+ab}+\frac{1}{ab}+\frac{1}{bc}+\frac{1}{ac}$