question_answer

If \[{{D}_{k}}\left| \begin{matrix}    1 & n & n  \\    2k & {{n}^{2}}+n+1 & {{n}^{2}}+n  \\    2k-1 & {{n}^{2}} & {{n}^{2}}+n+1  \\ \end{matrix} \right|\] and \[\sum\limits_{k=1}^{n}{{{D}_{k}}=56}\] then find value of n.

Answer:

7.00