<s>[INST] Show that $\frac {1}{3+x^2+y^2} + \frac {1}{3+y^2+z^2} +\frac{1} {3+x^2+z^2}\leq \frac {3}{5} . $ Let $x, y, z>0$ s.t. $x+y+z=3$.
Show that $$\frac {1}{3+x^2+y^2}  + \frac {1}{3+y^2+z^2} +\frac{1 } {3+x^2+z^2}\leq \frac {3}{5}\ . $$
My idea: $$3 + x^2 + y^2 \geq 1 + 2x+ 2y=7-2z $$
I notice that $f (t)=\frac {1}{7-2t} $  is a convex function but it's uselessness.
Also I have some troubles with the next inequality  $$\frac {a}{a^2+bc} +\frac {b}{b^2+ac}+\frac {c}{c^2+ab}\geq \frac {3}{2} \frac{a+b+c}{a^2+b^2+c^2} $$
My idea is to multiply and to apply Muirhead's inequality. But there are too much terms.
 [/INST] The second inequality.
By C-S we obtain:
$$\sum_{cyc}\frac{a}{a^2+bc}=\sum_{cyc}\frac{a^2(b+c)^2}{(a^3+abc)(b+c)^2}\geq$$
$$\geq\frac{\left(\sum\limits_{cyc}a(b+c)\right)^2}{\sum\limits_{cyc}(a^3+abc)(b+c)^2}=\frac{4(ab+ac+bc)^2}{\sum\limits_{cyc}(a^3+abc)(b+c)^2}.$$
Thus, it's enough to prove that
$$8(ab+ac+bc)^2(a^2+b^2+c^2)\geq3(a+b+c)\sum\limits_{cyc}(a^3+abc)(b+c)^2$$ or
$$\sum_{cyc}(5a^4b^2+5a^4c^2-6a^3b^3+4a^4bc-5a^3b^2c-5a^3c^2b+2a^2b^2c^2)\geq0,$$ which is obvious by Schur
$$\sum_{cyc}(a^4bc-a^3b^2c-a^3c^2b+a^2b^2c^2)\geq0$$ and Muirhead.
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