1/x+1-1/x+8=1/14 Giúp mk với Có 1 câu thôi

`1/(x+1) - 1/(x+8) = 1/14`

`<=> (14(x+8))/(14(x+1)(x+8)) - (14(x+1))/(14(x+1)(x+8)) = ((x+1)(x+8))/(14(x+1)(x+8))`

`<=> 14(x+8) - 14(x+1) = (x+1)(x+8)`

`<=> 14x + 112 - 14x - 14 = x^2 + 9x + 8`

`<=> x^2 + 9x - 90 = 0`

`<=> x^2 + 15x - 6x - 90 = 0`

`<=> x(x+15) - 6(x+15) = 0`

`<=> (x+15)(x-6) = 0`

`<=>` \(\left[ \begin{array}{l}x+15=0\\x-6=0\end{array} \right.\) 

`<=>` \(\left[ \begin{array}{l}x=-15\\x=6\end{array} \right.\) 

Vậy `S = {-15;6}`

`color[#33a4f5][ � phongOwO � ]`