Đáp án + Giải thích các bước giải:
`a)`
`(2x-1)(x+7)=x^2-49`
`<=> (2x-1)(x+7)-(x^2-49)=0`
`<=> (2x-1)(x+7)-(x-7)(x+7)=0`
`<=> (x+7)(2x-1-x+7)=0`
`<=> (x+7)(x+6)=0`
`<=>` \(\left[ \begin{array}{l}x+7=0\\x+6=0\end{array} \right.\) `<=>` \(\left[ \begin{array}{l}x=-7\\x=-6\end{array} \right.\)
Vậy `S={-7;-6}`
`b)`
`(2x+1)/(x-3)-x/(x+3)=1`
ĐKXĐ : `x ne +-3`
`<=> ((2x+1)(x+3)-x(x-3))/(x^2-9)=(x^2-9)/(x^2-9)`
`=> (2x+1)(x+3)-x(x-3)=x^2-9`
`<=> 2x^2+6x+x+3-x^2+3x-x^2+9=0`
`<=> 10x+12=0`
`<=> 10x=-12`
`<=> x=-6/5 \ \ (tmđk)`
Vậy `S={-6/5}`
`c)`
`(x+2)/3-(3x-1)/5<-2`
`<=> (5.(x+2)-3.(3x-1))/15< -30/15`
`=> 5.(x+2)-3.(3x-1)=-30`
`<=> 5x+10-9x+3<-30`
`<=> -4x<-30-3-10`
`<=> -4x<-43`
`<=> x>43/4`
Vậy `S={x|x>43/4}`