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hoamattroi_3520725127


Cho $a;b;c \in R^+$. Chứng minh bđt :
$\dfrac{1}{\sqrt{1 + a^2}} + \dfrac{1}{\sqrt{1 + b^2}} \ge \dfrac{2}{\sqrt{1 + (\dfrac{a + b}{2})^2}}$
$\dfrac{1}{\sqrt{1 + a^2}} + \dfrac{1}{\sqrt{1 + b^2}} \ge \dfrac{2}{\sqrt{1 + (\dfrac{a + b}{2})^2}}$