Đáp án:
$0$
Giải thích các bước giải:
$\begin{array}{l}
e)\dfrac{9}{{10}} - \dfrac{1}{{90}} - \dfrac{1}{{72}} - \dfrac{1}{{56}} - \dfrac{1}{{42}} - \dfrac{1}{{30}} - \dfrac{1}{{20}} - \dfrac{1}{{12}} - \dfrac{1}{6} - \dfrac{1}{2}\\
= \dfrac{9}{{10}} - \left( {\dfrac{1}{{10.9}} + \dfrac{1}{{9.8}} + \dfrac{1}{{8.7}} + \dfrac{1}{{7.6}} + \dfrac{1}{{6.5}} + \dfrac{1}{{5.4}} + \dfrac{1}{{4.3}} + \dfrac{1}{{3.2}} + \dfrac{1}{{2.1}}} \right)\\
= \dfrac{9}{{10}} - \left( {\dfrac{1}{9} - \dfrac{1}{{10}} + \dfrac{1}{8} - \dfrac{1}{9} + \dfrac{1}{7} - \dfrac{1}{8} + \dfrac{1}{6} - \dfrac{1}{7} + \dfrac{1}{5} - \dfrac{1}{6} + \dfrac{1}{4} - \dfrac{1}{5} + \dfrac{1}{3} - \dfrac{1}{4} + \dfrac{1}{2} - \dfrac{1}{3} + \dfrac{1}{1} - \dfrac{1}{2}} \right)\\
= \dfrac{9}{{10}} - \left( {1 - \dfrac{1}{{10}}} \right)\\
= \dfrac{9}{{10}} - \dfrac{9}{{10}}\\
= 0
\end{array}$
