Tính nhanh :-1 1/2.(-1 1/3).(-1 1/4)...(-1 1/1999)

* Hướng dẫn giải

$-1\frac{1}{2}.\left(-1\frac{1}{3}\right).\left(-1\frac{1}{4}\right)\mathrm{......}\left(-1\frac{1}{1999}\right)=\frac{-3}{2}.\frac{-4}{3}.\frac{-5}{4}\mathrm{.....}\frac{-2000}{1999}=1000$