\(S=1+\frac{1}{\left(\frac{3.2}{2}\right)}+\frac{1}{\left(\frac{4.3}{2}\right)}+\frac{1}{\left(\frac{5.4}{2}\right)}+...+\frac{1}{\left(\frac{9.8}{2}\right)}\)
\(=1+2\left(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{8.9}\right)\)
\(=1+2\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{8}-\frac{1}{9}\right)\)
\(=1+2\left(\frac{1}{2}-\frac{1}{9}\right)\)
\(=1+2.\frac{7}{18}\)
\(=1\frac{7}{9}\)
Chúc bn học tốt nhé!!! :)