\(\frac{1}{10\cdot11}+\frac{1}{11\cdot12}+.......+\frac{1}{19\cdot20}\)\(=\frac{1}{10}-\frac{1}{11}+\frac{1}{11}-\frac{1}{12}+.....+\frac{1}{18}-\frac{1}{19}\)\(+\frac{1}{19}-\frac{1}{20}\)
\(=\frac{1}{10}-\frac{1}{20}=\frac{2}{20}-\frac{1}{20}=\frac{1}{20}\)
K CHO MÌNH NHA CÁC BẠN
= 1/10-1/11+...+1/19-1/20
=1/10-1/20=1/10
A = \(\frac{1}{10\times11}+\frac{1}{11\times12}+...+\frac{1}{19\times20}\)
A = \(\frac{11-10}{10\times11}+\frac{12-11}{11\times12}+...+\frac{20-19}{19\times20}\)
A = \(\frac{1}{10}-\frac{1}{11}+\frac{1}{11}-\frac{1}{12}+...+\frac{1}{19}-\frac{1}{20}\)
A = \(\frac{1}{10}-\frac{1}{20}\)
A = \(\frac{1}{20}\)
A = 0,05
Nếu mình đúng thì các bạn k mình nhé
