Bài 3 Cho $a,b,c,d >0, \frac{1}{a}+ \frac{1}{b}+ \frac{1}{c}+ \frac{1}{d}=4 $
Chứng minh rằng:
$\sqrt[3]{\frac{a^3+b^3}{2}}+\sqrt[3]{\frac{b^3+c^3}{2}}+\sqrt[3]{\frac{c^3+d^3}{2}}+\sqrt[3]{\frac{d^3+a^3}{2}} \leq 2(a+b+c+d)-4 $
[RIGHT][I][B]Nguồn: MathScope.ORG[/B][/I][/RIGHT]