Đáp án:

`x∈{50;-60}`

Giải thích các bước giải:

`120/x-120/(x+10)=2/5`

`ĐKXĐ: x\ne0;x\ne-10`

`⇒(120.(x+10))/(x(x+10))-(120x)/(x(x+10))=2/5`

`⇒(120x+1200)/(x^2+10x)-(120x)/(x^2+10x)=2/5`

`⇒(120x+1200-120x)/(x^2+10x)=2/5`

`⇒1200/(x^2+10x)=1200/3000`

`⇒x^2+10x=3000`

`⇒x^2+10x-3000=0`

`⇒x^2+60x-50x-3000=0`

`⇒x(x+60)-50(x+60)=0`

`⇒(x-50)(x+60)=0`

$⇒\left[\begin{matrix} x-50=0\\ x+60=0\end{matrix}\right.$

$⇒\left[\begin{matrix} x=50\\ x=-60\end{matrix}\right.$

Vậy `x∈{50;-60}`

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