数学课前练习

1. 若两个等差数列\(\{a_n\}\)、\(\{b_n\}\)的前\(n\)项和分别为\(A_n\)、\(B_n\)，且满足\(\displaystyle \frac{A_n}{B_n} = \displaystyle \frac{4n + 2}{5n - 5}\)，则\(\displaystyle \frac{a_5 + a_{13}}{b_5 + b_{13}}\)的值为( )

A. \(\displaystyle \displaystyle \frac{7}{9}\)

B. \(\displaystyle \displaystyle \frac{8}{7}\)

C. \(\displaystyle \displaystyle \frac{19}{20}\)

D. \(\displaystyle \displaystyle \frac{7}{8}\)

2. 公差为\(d\)的等差数列\(\{a_n\}\)，前\(n\)项和为\(S_n\)，\(S_{11} > 0\)，\(S_{12} < 0\)，下列说法正确的有( )

A. \(d < 0\)

B. \(a_7 > 0\)

C. \(\{S_n\}\)中\(S_5\)最大

D. \(|a_4| < |a_9|\)