kekhonghon2

$\left.\begin{matrix} 2x=3y\\ 7z=5y \end{matrix}\right\}\Rightarrow 2x*7z*y=3y*5y*y \Leftrightarrow 14xyz=15y^3\Leftrightarrow 15y^3=23928\Leftrightarrow y=\sqrt[3]{\frac{7976}{5}}\Rightarrow \left\{\begin{matrix} x=\sqrt[3]{\frac{26919}{5}}\\ z=\sqrt[3]{\frac{2735768}{625}} \end{matrix}\right.$

$\frac{x}{2}=\frac{y}{3}=\frac{z}{4}\Rightarrow \frac{x^2}{4}=\frac{y^2}{9}=\frac{2z^2}{32}=\frac{x^2-y^2+2z^2}{4-9+32}=\frac{108}{27}\Rightarrow \left\{\begin{matrix} x^2=16\\ y^2=36\\ z^2=64 \end{matrix}\right.\Rightarrow \begin{matrix} \left\{\begin{matrix} x=4\\ y=6\\ z=8 \end{matrix}\right.\\ \left\{\begin{matrix} x=-4\\ y=-6\\ z=-8 \end{matrix}\right. \end{matrix}$