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

* Hướng dẫn giải

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