Question

[Quản gia Whisper]

Tính tổng dãy p/s sau

\(A=\frac{5}{10.11}+\frac{5}{11.12}+\frac{5}{12.13}+......+\frac{5}{99.100}\)

Answer 1

[Trần Thùy Trang]

cậu kia làm sai rùi

A .1/5 = 1/10.11+1/11.12+1/12.13+...+1/99,100

A . 1/5 = 1/10-1/11+1/11-1/12+...+1/99-1/100

A .1/5 = 1/10-1/100

A.1/5 = 9/199

A = 9/20

k nhé

Answer 2

[Quản gia Whisper]

\(A=\frac{5}{10.11}+\frac{5}{11.12}+\frac{5}{12.13}+.....+\frac{5}{99.100}\)

=\(\frac{5}{10}-\frac{5}{11}+\frac{5}{11}-\frac{5}{12}+\frac{5}{12}-\frac{5}{13}\)

=\(\frac{5}{10}-\frac{5}{100}=\frac{45}{100}\)=\(\frac{9}{20}\)