Đáp án:
Giải thích các bước giải:
$\dfrac{100}{x}-\dfrac{100}{x-20}=\dfrac{5}{12}$
$ $
$⇔\dfrac{100.(x-20)}{x.(x-20)}-\dfrac{100x}{x.(x-20)}=\dfrac{5}{12}$
$ $
$⇔\dfrac{100x-2000}{x.(x-20)}-\dfrac{100x}{x.(x-20)}=\dfrac{5}{12}$
$ $
$⇔\dfrac{(100x-2000)-100x}{x.(x-20)}=\dfrac{5}{12}$
$ $
$⇔\dfrac{-2000}{x.(x-20)}=\dfrac{5}{12}$
$ $
$⇔-24000=5.[x.(x-20)]$
$⇔x.(x-20)=-4800$
$⇔x^{2}-20x=-4800$
$⇔x^{2}-2.x.10+4800=0$
$⇔x^{2}-2.x.10+10^{2}+4700$
$⇔(x-10)^{2}=-4700$
Vay pt vo nghiem
