\(\Rightarrow\)S\(=\)9/22 nha bạn,mình tính nhần
\(\frac{10}{11}\)nha bạn mình giải rồi
S\(=\)1/2.3 + 1/3.4 + 1/4.5 + 1/5.6 + 1/6.7 + 1/7.8 + 1/8.9 + 1/9.10 + 1/10.11
\(\rightarrow\)S\(=\)1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10+1/10-1/11
\(\rightarrow\)S\(=\)1/2-1/11
\(\rightarrow\)S\(=\)11/22-2/22
\(\Rightarrow\)S\(=\)7/22