Bài 2 : cho a, b, c> 0
1 ) \(\frac{a^2}{b+c}+\frac{b^2}{c+a}+\frac{c^2}{a+c}\ge\frac{a+b+c}{2}\)
2) \(\frac{bc}{a}+\frac{ac}{b}+\frac{ab}{c}\ge a+b+c\)
3 ) \(\frac{ab}{a+b}+\frac{bc}{b+c}+\frac{ca}{c+a}\le\frac{a+b+c}{2}\)
4) \(\frac{a^2}{b}+\frac{b^2}{c}+\frac{c^2}{a}\ge a+b+c\)