Question

1+\(\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+\frac{1}{15}+\frac{1}{21}+\frac{1}{28}+\frac{1}{36}+\frac{1}{45}\)

Answer 1

\(=1+\frac{1}{1.3}+\frac{1}{3.2}+\frac{1}{2.5}+\frac{1}{5.3}+\frac{1}{3.7}+\frac{1}{7.4}+\frac{1}{4.9}+\frac{1}{9.5}\)

\(=1+1-\frac{1}{5}\)

\(=\frac{10}{5}-\frac{1}{5}\)

\(=\frac{9}{5}\)

Ai thấy đúng thì

Answer 2

ra 9/5 bạn nhé

k cho mk mk kb 

Answer 3

\(\frac{9}{5}nha\)

Answer 4

= 1 + 1 - 1/5

= 10/5 - 1/5

= 9/5

Đs: 9/5

Answer 5

ồ, câu hỏi này hay đấy chứ

đặt A = \(\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+\frac{1}{15}+\frac{1}{21}+\frac{1}{28}+\frac{1}{36}+\frac{1}{45}\)

A = \(\frac{2}{2.3}+\frac{2}{2.6}+\frac{2}{2.10}+\frac{2}{2.15}+\frac{2}{2.21}+\frac{2}{2.28}+\frac{2}{2.36}+\frac{2}{2.45}\)

A = \(\frac{2}{6}+\frac{2}{12}+\frac{2}{20}+\frac{2}{30}+\frac{2}{42}+\frac{2}{56}+\frac{2}{72}+\frac{2}{90}\)

A = \(\frac{2}{2.3}+\frac{2}{3.4}+\frac{2}{4.5}+\frac{2}{5.6}+\frac{2}{6.7}+\frac{2}{7.8}+\frac{2}{8.9}+\frac{2}{9.10}\)

A = \(2.\left(\frac{1}{2}-\frac{1}{3}\right)+2.\left(\frac{1}{3}-\frac{1}{4}\right)+2.\left(\frac{1}{4}-\frac{1}{5}\right)+2.\left(\frac{1}{5}-\frac{1}{6}\right)+2.\left(\frac{1}{6}-\frac{1}{7}\right)+2.\left(\frac{1}{7}-\frac{1}{8}\right)+2.\left(\frac{1}{8}-\frac{1}{9}\right)+2.\left(\frac{1}{9}-\frac{1}{10}\right)\)A = \(2.\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\right)\)

A = \(2.\left(\frac{1}{2}-\frac{1}{10}\right)\)

A = \(2.\frac{2}{5}\)

A = \(\frac{4}{5}\)

\(\Rightarrow1+\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+\frac{1}{15}+\frac{1}{21}+\frac{1}{28}+\frac{1}{36}+\frac{1}{45}=1+\frac{4}{5}=\frac{9}{5}\)