Cho a,b,c,d dương. Chứng minh rằng:
$2\sqrt{\frac{3a}{a+b+c}}+3\sqrt[3]{\frac{bc}{\left ( a+b \right)\left ( a+c+b+d \right )}}+4\sqrt[4]{\frac{2b^{3}d}{81\left ( a+b)^{3}\left ( a+b+c+d \right ) \right )}}\leq \frac{25}{6}$