Question

Tính nhanh :       (1-1/99) nhân (1-1/100) nhân ..... nhân (1-1/2006)

 

Answer 1

Ta có : \(\left(1-\frac{1}{99}\right)\text{ x }\left(1-\frac{1}{100}\right)\text{ x }.....\text{ x }\left(1-\frac{1}{2006}\right)\)

\(=\frac{98}{99}\text{ x }\frac{99}{100}\text{ x }\frac{100}{101}\text{ x }......\text{ x }\frac{2005}{2006}\)

\(=\frac{98\text{ x }99\text{ x }100\text{ x }......\text{ x }2005}{99\text{ x }100\text{ x }101\text{ x }......\text{ x }2006}\)

\(=\frac{98}{2006}=\frac{49}{1003}\)