Đặt `x/2=y/3=z/5=K`
`-> x=2K, y=3K, z=5K`
`=> xyz=-30=> 2K*3K*5K=-30`
`-> 30K^3=-30`
`-> K^3=-30 \div 30`
`-> K^3=-1`
`-> K^3=-1^3`
`-> K=-1`
Với `K=-1`
`-> x=2*-1=-2` `, y=3*-1=-3` `, z=5*-1=-5`
Vậy, \(\left\{{}\begin{matrix}x=-2\\y=-3\\z=-5\end{matrix}\right.\)