1, Biết $a^2+b^2+c^2=3. CMR: \frac{ab}{c}+\frac{bc}{a}+\frac{ca}{b} \geq 3$
2, CMR: a,b,c>0 thì:
$B=\frac{a}{2a+b+c}+\frac{b}{a+2b+c}+\frac{c}{a+b+2c} \leq \frac{3}{4}$
3,CMR: $ \frac{a}{b+c}+\frac{b}{c+a}+\frac{c}{a+b} \geq \frac{a}{1+a^2}+\frac{b}{1+b^2}+\frac{c}{1+c^2}$