hanhtrinhtuonglai

$\left\{\begin{matrix} x^4-y^4=240 & \\x^3-2y^3=3(x^2-4y^2)-4(x-8y) & \end{matrix}\right.$

 Cho $ a,b,c>0$

Chứng minh  rằng

$ \sqrt {{\frac {a}{a+b}}}+\sqrt {{\frac {b}{b+c}}}+\sqrt {{\frac {c}{c+ a}}}$$\leq$$ 3/\sqrt {2}$