Bài 2:\frac{a^3}{b^2}+a\geq 2\frac{a^2}{b} (Cô-Si),Tương tự \frac{b^3}{c^2}+b\geq 2\frac{b^2}{a},\frac{c^3}{a^2}+c\geq \frac{c^2}{a}
\Rightarrow \frac{a^3}{b^2}+\frac{b^3}{c^2}+\frac{c^3}{a^2}\geq 2(\frac{a^2}{b}+\frac{b^2}{c}+\frac{c^2}{a})-(a+b+c)
Có (\frac{a^2}{b}+b)+(\frac{b^2}{c}+c)+(\frac{c^2}{a}+a)\geq 2(a+b+c)\Leftrightarrow\frac{a^2}{b}+\frac{b^2}{c}+\frac{c^2}{a}\geq(a+b+c)
\Rightarrow ĐPCM