Thực hiện phép tính: e) (2 x ^2 − 20 x + 50)/( 3 x + 3) ⋅( x^ 2 − 1)/ 4 ( x − 5 ) ^3 .

e) \[\frac{{2{x^2} - 20x + 50}}{{3x + 3}} \cdot \frac{{{x^2} - 1}}{{4{{\left( {x - 5} \right)}^3}}}\]

\[ = \frac{{2{{\left( {x - 5} \right)}^2}}}{{3\left( {x + 1} \right)}} \cdot \frac{{\left( {x - 1} \right)\left( {x + 1} \right)}}{{4{{\left( {x - 5} \right)}^3}}} = \frac{{x - 1}}{{6\left( {x - 5} \right)}}.\]