Tìm x, biết: 2/1^2.6/2^2.12/3^2=-20

Lời giải:

\(\frac{2}{{{1^2}}}.\frac{6}{{{2^2}}}.\frac{{12}}{{{3^2}}}.\frac{{20}}{{{4^2}}}.....\frac{{110}}{{{{10}^2}}}.x =  - 20\)

\(\begin{array}{l}\frac{{1.2}}{{{1^2}}}.\frac{{2.3}}{{{2^2}}}.\frac{{3.4}}{{{3^2}}}.\frac{{4.5}}{{{4^2}}}.....\frac{{10.11}}{{{{10}^2}}}.x =  - 20\\\frac{2}{1}.\frac{3}{2}.\frac{4}{3}.\frac{5}{4}....\frac{{11}}{{10}}.x =  - 20\\11.x =  - 20\\x = \frac{{ - 20}}{{11}}\end{array}\)

Vậy \(x = \frac{{ - 20}}{{11}}\)