Cho các số a,b,c dương CMR:
@@4:
$\frac{ab}{a^{2}+b^{2}+ab}+\frac{bc}{b^{2}+c^{2}+bc}+\frac{ca}{c^{2}+a^{2}+ca}\leq 1$
$\frac{ab}{a^{2}+b^{2}+ab}+\frac{bc}{b^{2}+c^{2}+bc}+\frac{ca}{c^{2}+a^{2}+ca}$
$\leq \frac{ab}{\frac{3}{4}(a+b)^2}+\frac{bc}{\frac{3}{4}(c+b)^2}+\frac{ca}{\frac{3}{4}(c+a)^2}$
$\leq \frac{\frac{1}{4}(a+b)^2}{\frac{3}{4}(a+b)^2}+\frac{\frac{1}{4}(b+c)^2}{\frac{3}{4}(c+b)^2}+\frac{\frac{1}{4}(c+a)^2}{\frac{3}{4}(c+a)^2}$
$\leq 1$
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