`a, 12/-6 = x/5 = -y/3 = z/-17 = t/9`

`-2=x/5=-y/3=z/-17=t/9`

`=>`$\begin{cases} \frac{x}{5} =-2\\ \frac{-y}{3}=-2\\ \frac{z}{-17}=-2\\ \frac{t}{9}=-2 \end{cases}$ 

`=>`  $\begin{cases} x=-2.5=10\\y=-2.(-3)=6\\z=-2(-17)=34\\t=-2.9=-18 \end{cases}$

Vậy  $\begin{cases} x=10\\y=-6\\z=34\\t=-18 \end{cases}$

`b,( -24)/-6 = x/3 = 4/(y²) = (z³)/-2 `

`4=x/3=4/y^2=z^3/-2`

`x/3 = 4 → x = 12`

`4/(y² )= 4 → y² = 1 → y =` $\pm$`1`

`(z³)/-2 = 4 → z³ = -8 → z = -2`

Vậy `x=12;y=`$\pm$`1``;z=-2`