Đáp án:
Giải thích các bước giải:
$\dfrac{1}{5.8}+\dfrac{1}{8.11}+...+\dfrac{1}{x.(x+3)}=\dfrac{101}{1540}$
$⇔\dfrac{1}{3}.(\dfrac{3}{5.8}+\dfrac{3}{8.11}+...+\dfrac{3}{x.(x+3)}=\dfrac{101}{1540}$
$ $
$⇔\dfrac{1}{5}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{11}+...+\dfrac{1}{x}-\dfrac{1}{x+3}=\dfrac{303}{1540}$
$ $
$⇔\dfrac{1}{5}-\dfrac{1}{x+3}=\dfrac{303}{1540}$
$ $
$⇔\dfrac{1}{x+3}=\dfrac{1}{308}$
$ $
$⇒x+3=308$
$⇒x=305$
