Вычисли и запиши ответ

\({\left (\dfrac{17}{18}\cdot \dfrac{19}{20} \right )\cdot \left (\dfrac{18}{19}\cdot \dfrac{20}{21} \right )\raisebox{-1.5em}{\),\(}\mathrlap{\,=}}\) \({=\left (\dfrac{17}{18}\cdot \dfrac{18}{19} \right )\cdot \left (\dfrac{19}{20}\cdot \dfrac{20}{21} \right )\raisebox{-1.5em}{\),\(}\mathrlap{\,=}}\) \({=\dfrac{17}{19}\cdot \dfrac{19}{21}=\dfrac{17}{21}}\) .

В ответе запиши несократимую дробь.

\({\left (\dfrac{63}{64}\cdot \dfrac{65}{66} \right )\cdot \left (\dfrac{64}{65}\cdot \dfrac{66}{67} \right )\raisebox{-1.5em}{\),\(}\mathrlap{\,\cdot}}\) \({\cdot \left (\dfrac{67}{68}\cdot \dfrac{69}{70} \right )\cdot \left (\dfrac{68}{69}\cdot \dfrac{70}{71} \right )=}\) [ ].