Đáp án:
`S \ = \ { \ 20 \ ; \ -25 \ }`
Giải thích các bước giải:
`300/x - 300/(x+5) = 3`
ĐKXĐ : `x ne 0 ; -5`
`<=> (300(x+5)-300x)/(x(x+5)) = (3x(x+5))/(x(x+5))`
`=> 300(x+5)-300x=3x(x+5)`
`<=> 300x+1500-300x=3x^2+15x`
`<=> 3x^2+15x-1500=0`
`<=> x^2+5x-500=0`
`<=> x^2-20x+25x-500=0`
`<=> x.(x-20)+25.(x-20)=0`
`<=> (x+25).(x-20)=0`
`<=>` \(\left[ \begin{array}{l}x+25=0\\x-20=0\end{array} \right.\) `<=>` \(\left[ \begin{array}{l}x=-25 \ \ \rm (tm)\\x=20 \ \ \rm (tm)\end{array} \right.\)
Vậy `S \ = \ { \ 20 \ ; \ -25 \ }`
