Tìm min của các biểu thức sau:
- P = $\sqrt[4]{\frac{a}{b+c}}$ + $\sqrt[4]{\frac{b}{c+a}}$ + $\sqrt[4]{\frac{c}{a+b}}$ + $\sqrt{\frac{b+c}{a}}$ + $\sqrt{\frac{c+a}{b}} + \sqrt{\frac{a+b}{c}}$
- cho a$\in$$\begin{bmatrix} -1;1 \end{bmatrix}$ . S= $a^5-3a^4+a^3+8a^2-14a+\frac{1}{a^3-a^2-3a+4}$
- cho a$\in$[-2;2]. S= $a^5-7a^4+13a^3+14a^2-72a+\frac{1}{a^3-3a^2-4a+13}$
- cho a$\in [-\sqrt{3};\sqrt{3}]$ . S= $\frac{a^6-10a^5+19a^4+62a^3-151a^2-96a+257}{a^3-5a^2-3a+16}$