Question

[Lê Thùy Linh]

Tính tổng:a)3+3/5+3/25+3/125+3/625

b)M=4/3.7+4/7.11+4/11.15+...+8/95.99

c)N=1/2+1/6+1/12+1/20+...+1/90

Answer 1

[»βέ•Ҫɦαηɦ«]

Ta có : \(M=\frac{4}{3.7}+\frac{4}{7.11}+\frac{4}{11.15}+.....+\frac{4}{95.99}\)

\(=\frac{1}{3}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+......+\frac{1}{95}-\frac{1}{99}\)

\(=\frac{1}{3}-\frac{1}{99}\)

\(=\frac{32}{99}\)