Giải thích các bước giải:
\(\begin{array}{l}
{U_n} = \frac{{2{n^2} - 1}}{{{n^2} + 1}}\\
\to {U_1} = \frac{{{{2.1}^2} - 1}}{{{1^2} + 1}} = \frac{1}{2}\\
{U_2} = \frac{{{{2.2}^2} - 1}}{{{2^2} + 1}} = \frac{7}{5}\\
{U_3} = \frac{{{{2.3}^2} - 1}}{{{3^2} + 1}} = \frac{{17}}{{10}}\\
{U_4} = \frac{{{{2.4}^2} - 1}}{{{4^2} + 1}} = \frac{{31}}{{17}}\\
{U_5} = \frac{{{{2.5}^2} - 1}}{{{5^2} + 1}} = \frac{{49}}{{26}}\\
{U_{200}} = \frac{{{{2.200}^2} - 1}}{{{{200}^2} + 1}} = \frac{{79999}}{{40001}}
\end{array}\)
