\(S=\frac{5}{1.3}+\frac{5}{3.5}+\frac{5}{5.7}+..+\frac{5}{97.99}\)
\(=\frac{5}{2}.\left(5+\frac{5}{3}+\frac{5}{5}+\frac{5}{7}+...+\frac{5}{97}+\frac{5}{99}\right)\)
\(=\frac{5}{2}.\left(5+\frac{5}{99}\right)\)
\(=\frac{5}{2}.\frac{500}{99}\)
\(=\frac{1250}{99}\)(có gì sai sót xin bỏ qua cho T^T)
\(S=\frac{5}{1.3}+\frac{5}{3.5}+\frac{5}{5.7}+...+\frac{5}{97.99}\)
\(S=\frac{5}{2}.\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{97}-\frac{1}{99}\right)\)
\(S=\frac{5}{2}.\left(1-\frac{1}{99}\right)\)
\(S=\frac{5}{2}.\frac{98}{99}\)
\(S=\frac{230}{99}\)
Chúc bạn hok tốt
~k cho mình nhé ~
kb nữa
