Question

tính nhanh

1/6+ 1/12+1/20+1/30+. . .+1/90+1/110

giúp mình nhé giải tất ra cho tớ

Answer 1

Bằng \(\frac{9}{22}\)nha bạn.

Answer 2

\(\frac{1}{2.3}+\frac{1}{3.4}+....+\frac{1}{10.11}\)

=\(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-......+\frac{1}{10}-\frac{1}{11}.\)

=\(\frac{1}{2}-\frac{1}{11}\)

=\(\frac{9}{22}.\)

Answer 3

\(\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+...+\frac{1}{90}+\frac{1}{110}\)

\(=\frac{1}{2\times3}+\frac{1}{3\times4}+\frac{1}{4\times5}+\frac{1}{5\times6}+...+\frac{1}{9\times10}+\frac{1}{10\times11}\)

\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-...-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}+\frac{1}{10}-\frac{1}{11}\)

\(=\frac{1}{2}-\frac{1}{11}\)

\(=\frac{9}{22}\)