a,5x=2
<=>x=$\frac{2}{5}$
vậy S={$\frac{2}{5}$ }
b,\(\left[ \begin{array}{l}x+2=0\\3x-5=0\end{array} \right.\)
=>\(\left[ \begin{array}{l}x=-2\\x=$\frac{5}{3}$\end{array} \right.\)
vậy S={-2;$\frac{5}{3}$}
c,$\frac{3y-1}{y-1}$+3=$\frac{1}{y-1}$ đkxđ:y$\neq$ 1
<=>$\frac{3y-1}{y-1}$+$\frac{3(y-1)}{y-1}$=$\frac{1}{y-1}$
<=>3y-1+3y-3=1
<=>6y-4=1
<=>6y-5=0
<=>6y=5
<=>y=$\frac{5}{6}$(TMĐKXĐ)
vậy S={$\frac{5}{6}$}