Bài tập 10 trang 105 SGK Toán 11 NC

a) Ta có:

\(\begin{array}{l}
{u_2} = \frac{2}{{u_1^2 + 1}} = 2\\
{u_3} = \frac{2}{{u_2^2 + 1}} = \frac{2}{{{2^2} + 1}} = \frac{2}{5}\\
{u_4} = \frac{2}{{u_3^2 + 1}} = \frac{2}{{{{\left( {\frac{2}{5}} \right)}^2} + 1}} = \frac{{50}}{{29}}\\
{u_5} = \frac{2}{{u_4^2 + 1}} = \frac{2}{{{{\left( {\frac{{50}}{{29}}} \right)}^2} + 1}} = \frac{{1682}}{{3341}}
\end{array}\)

b) Ta có:

\(\begin{array}{l}
{u_3} = {u_2} - 2{u_1} =  - 2 - 2.1 =  - 4\\
{u_4} = {u_3} - 2{u_2} =  - 4 - 2.\left( { - 2} \right) = 0\\
{u_5} = {u_4} - 2{u_3} = 0 - 2.\left( { - 4} \right) = 8
\end{array}\)

-- Mod Toán 11 HỌC247