Bài 1:
$\frac{a}{a+\sqrt{2015+bc}}$ $= \frac{a}{a+\sqrt{a(a+b+c)}+bc}$ $= \frac{a}{a+\sqrt{(a+b)(a+c)}}$
$\leq \frac{a}{a+\sqrt{a}(\sqrt{b}+\sqrt{c})}$ $= \frac{\sqrt{a}}{\sqrt{a}+\sqrt{b}+\sqrt{c}}$
( Do Áp dụng BĐT Bu-nhi-a: $(a+b)(a+c) \geqslant(\sqrt{a}.\sqrt{b}+\sqrt{a}.\sqrt{c})^{2}$
$\Rightarrow$ $\sqrt{(a+b)(a+c)}\geqslant \sqrt{a}.\sqrt{b}+\sqrt{a}.\sqrt{c}$ )
Tương tự: $\frac{b}{b+\sqrt{2015b+ac}}\leqslant \frac{\sqrt{b}}{\sqrt{a}+\sqrt{b}+\sqrt{c}}$
$\frac{c}{c+\sqrt{2015c+ab}}\leq \frac{\sqrt{c}}{\sqrt{a}+\sqrt{b}+\sqrt{c}}$
Cộng 3 BĐT trên vế theo vế $\Rightarrow đpcm$
Dấu = xảy ra khi a = b = c = 2015/3