Question

\(\frac{1}{1.2}.x+\frac{1}{2.3}.x.........+\frac{1}{9.10}=\frac{18}{5}\)

Answer 1

\(\frac{1}{9.10}\)có x k bn?

k có x như trên đề thì hơi vl đấy.

phiền bn xem lại.

Answer 2

\(\frac{1}{1\cdot2}\times+\cdot\cdot\cdot+\frac{1}{9\cdot10}\times=\frac{18}{5}\)

\(\Rightarrow\left(\frac{1}{1\cdot2}+\cdot\cdot\cdot+\frac{1}{9\cdot10}\right)\times=\frac{18}{5}\)

\(\Rightarrow\left(1-\frac{1}{2}+\cdot\cdot\cdot+\frac{1}{9}-\frac{1}{10}\right)\times=\frac{18}{5}\)

\(\Rightarrow\left(1-\frac{1}{10}\right)\times=\frac{18}{5}\)

\(\Rightarrow\frac{9}{10}\times=\frac{18}{5}\)

\(\Rightarrow\times=\frac{18}{5}:\frac{9}{10}\)

\(\Rightarrow\times=4\)