\(\frac{1}{1.2.3}+\frac{1}{2.3.4}+...+\frac{1}{2004.2005.2006}\)
\(=\frac{1}{2}\left(\frac{1}{1.2}-\frac{1}{2.3}+\frac{1}{2.3}-\frac{1}{3.4}+...+\frac{1}{2004.2005}-\frac{1}{2005.2006}\right)\)
\(=\frac{1}{2}\left(\frac{1}{2}-\frac{1}{2005.2006}\right)\)
\(=\frac{1}{4}-\frac{1}{2.2005.2006}\)
\(\frac{2}{1.2.3}\) + \(\frac{2}{2.3.4}\) + ..... + \(\frac{2}{2004.2005.2006}\)
\(\dfrac{1}{1.2.3}+\dfrac{1}{2.3.4}+...+\dfrac{1}{2004.2005.2006}\)
Tính1/ 1.2.3+ 1/ 2.3.4+ ....... +1/2004.2005.2006
\(\frac{1}{1.2.3}+\frac{1}{2.3.4}+\frac{1}{4.5.6}+......+\frac{1}{98.99.100}\)
\(\frac{1}{1.2.3}.\frac{1}{2.3.4}.\frac{1}{3.4.5}...\frac{1}{98.99.100}\)
Tính:\(\frac{1}{1.2.3}+\frac{1}{2.3.4}+\frac{1}{3.4.5}+...+\frac{1}{2018.2019.2020}.\)
C= \(\frac{1}{1.2.3}+\frac{1}{2.3.4}+\frac{1}{3.4.5}+...+\frac{1}{11.12.13}\)
Tính nhanh\(\frac{1}{1.2.3}+\frac{1}{2.3.4}+\frac{1}{3.4.5}+...+\frac{1}{37.38.39}\)
\(A=\frac{1}{1.2.3}-\frac{1}{2.3.4}-.....-\frac{1}{97.98.99}\)
