c/
`3x^2 -16x +5 =0`
`<=> 3x^2 - x - 15x +5 =0`
`<=> x(3x - 1) - 5(3x -1) =0`
`<=> (x-5)(3x-1) =0`
`<=>` \(\left[ \begin{array}{l}x-5=0\\3x-1=0\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=5\\x=\dfrac{1}{3}\end{array} \right.\)
Vậy `x \in {5 ; 1/3}`
d/
`3x^2 -12x =0`
`<=> 3x(x - 4) =0`
`<=>` \(\left[ \begin{array}{l}3x=0\\x-4 =0\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=0\\x=4\end{array} \right.\)
Vậy `x \in { 0 ;4}`
