Bài tập 4.12 trang 157 SBT Toán 11

Ta có:
\(\begin{array}{l}
a = 34 + \frac{{12}}{{{{10}^2}}} + \frac{{12}}{{{{10}^4}}} + \frac{{12}}{{{{10}^6}}} + ... = 34 + 12.\left( {\frac{1}{{{{10}^2}}} + \frac{1}{{{{10}^4}}} + .. + \frac{1}{{{{10}^n}}} + ...} \right)\\
 = 34 + 12.\frac{{\frac{1}{{{{10}^2}}}}}{{1 - \frac{1}{{{{10}^2}}}}} = 34 + \frac{{12}}{{99}} = \frac{{1126}}{{33}}
\end{array}\)

-- Mod Toán 11 HỌC247