Question

A = \(\frac{1}{1.2}\)+\(\frac{1}{2.3}\)+\(\frac{1}{3.4}\)+...+ \(\frac{1}{9.10}\)là:

Answer 1

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

Answer 2

bạn nói rõ câu trả lời ra dc ko

Answer 3

\(A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{9.10}\)\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}\)

\(A=1-\frac{1}{10}=\frac{9}{10}\)