Cách làm cho bạn:
$(\frac{1}{2}+1) (\frac{1}{3}+1)(\frac{1}{4}+1)...(\frac{1}{999}+1)$
$= (\frac{1}{2}+\frac{2}{2}) (\frac{1}{3}+\frac{3}{3})(\frac{1}{4}+\frac{4}{4})...(\frac{1}{999}+\frac{999}{999})$
$= \frac{3}{2}\times \frac{4}{3}\times \frac{5}{4}\times ...\times \frac{1000}{999}$
$= \frac{1000}{2}$
$= 500$
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