$\text{Đáp án + Giải thích các bước giải:}$
`c//(x+3)/(3x+1)+(5)/(1-3x)=(3x^{2}-4x)/(9x^{2}-1)` `(ĐKXĐ:x\ne±(1)/(3))`
`<=>((x+3)(1-3x))/((3x+1)(1-3x))+(5(3x+1))/((1-3x)(3x+1))=-(3x^{2}-4x)/((3x+1)(1-3x))`
`=>(x+3)(1-3x)+5(3x+1)=-(3x^{2}-4x)`
`<=>x-3x^{2}+3-9x+15x+5+3x^{2}-4x=0`
`<=>(3x^{2}-3x^{2})+(x-9x+15x-4x)+(3+5)=0`
`<=>3x+8=0`
`<=>3x=-8`
`<=>x=-(8)/(3)(TM)`
`\text{Vậy}` `S={-(8)/(3)}`
`d//9x^{2}=(3x+2)(x-3)+4`
`<=>9x^{2}=3x^{2}-9x+2x-6+4`
`<=>9x^{2}=3x^{2}-7x-2`
`<=>9x^{2}-3x^{2}+7x+2=0`
`<=>6x^{2}+7x+2=0`
`<=>(6x^{2}+4x)+(3x+2)=0`
`<=>2x(3x+2)+(3x+2)=0`
`<=>(3x+2)(2x+1)=0`
`<=>` \(\left[ \begin{array}{l}3x+2=0\\2x+1=0\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}3x=-2\\2x=-1\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=-\dfrac{2}{3}\\x=-\dfrac{1}{2}\end{array} \right.\)
`\text{Vậy}` `S={-(2)/(3);-(1)/(2)}`
