Merge pull request #65 from neggor/patch-1

Update exercise 2.4.9 chapter2-4.tex

chapters/chapter2/chapter2-4.tex

@@ -271,7 +271,7 @@ \section{The Monotone Convergence Theorem and a First Look at Infinite Series}
   \begin{aligned}
   s_n
   &=   b_1 + b_2 + (b_3 + b_4) + \dots + (b_{2^{k-1}} + \dots + b_{2^k}) \\
-  &\le b_1 + b_2 + (b_4 + b_4) + \dots + 2^{k-1}b_{2^k}
+  &\ge b_1 + b_2 + (b_4 + b_4) + \dots + 2^{k-1}b_{2^k}
   \end{aligned}
   $$
   (Notice there are $2^k - 2^{k-1} = 2^{k-1}$ terms in the last term)