$x,\,y,\,z\geqq 0$. Chứng minh rằng:
$$J= \frac{9}{8}\,y^{2}\left ( 2x-y \right )^{2}+ \frac{1}{16}\left ( 2x-y \right )^{4}+ \frac{1}{2}\,y\left ( 2x-y \right )^{3}+ \frac{1}{16}\left ( 16y^{3}z- 59y^{4} \right )\leqq xz\left( xy+ zx+ 2y^{2} \right )$$
