Đáp án:
`x=9999`
Giải thích các bước giải:
$\rm\dfrac{x}{2}+\dfrac{x}{6}+\dfrac{x}{12}+...+\dfrac{x}{9702}=9898\\⇒x . \dfrac{1}{2}+x . \dfrac{1}{6}+x . \dfrac{1}{12}+...+ x . \dfrac{1}{9702}=9898\\⇒x.\left(\dfrac{1}{2}+\dfrac{1}{6}+\dfrac{1}{12}+...+\dfrac{1}{9702}\right)=9898\\⇒x.\left(\dfrac{1}{1.2}+\dfrac{1}{2.3}+\dfrac{1}{3.4}+...+\dfrac{1}{98.99}\\⇒x.\left(\dfrac{1}{1}-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{98}-\dfrac{1}{99}\right.\right)=9898\\⇒x.\left(\dfrac{1}{1}-\dfrac{1}{99}\right)=9898\\⇒x.\left(\dfrac{99}{99}-\dfrac{1}{99}\right)=9898\\⇒x.\dfrac{99-1}{99} =9898\\⇒x.\dfrac{98}{99}=9898\\⇒x=9898:
\dfrac{98}{99}\\⇒x=9898.\dfrac{99}{98}\\⇒x=\dfrac{9898.99}{98}\\=>x=\dfrac{98.101.99}{98}\\⇒x=\dfrac{1.101.99}{1}\\⇒x=101.99\\⇒x=9999\\Vậy \ x \ = \ 9999$
