update notations and fix typos

pages/Math4111/Math4111_L21.md

@@ -56,7 +56,7 @@ $$
 \end{aligned}
 $$
 
-EOP
+QED
 
 #### Theorem 3.42 (Dirichlet's test)
 
@@ -101,7 +101,7 @@ $$
 
 So $\sum a_nb_n$ converges.
 
-EOP
+QED
 
 #### Theorem 3.43 (Alternating series test)
 
@@ -122,7 +122,7 @@ So $|A_n|\leq 1$ for all $n\in \mathbb{N}$.
 
 By Theorem 3.42, $\sum_{n=1}^\infty a_n b_n$ converges.
 
-EOP
+QED
 
 Example:
 
@@ -161,7 +161,7 @@ So $|A_n|\leq \frac{2}{|1-z|}$ for all $n\in \mathbb{N}$.
 
 By Dirichlet's test, $\sum_{n=0}^\infty b_nz^n$ 
 
-EOP
+QED
 
 ### Absolute convergence
 
@@ -183,7 +183,7 @@ $$
 \sum_{n=0}^\infty |a_n|\geq \sum_{n=0}^\infty a_n
 $$
 
-EOP
+QED
 
 Rearrangement of series:
 
@@ -257,4 +257,4 @@ For every $n\in \mathbb{N}$, there exists a $p$ such that $\{1,2,\cdots,n\}\subs
 
 Then $|s_n-t_n|\leq \sum_{k=N+1}^\infty |a_k|$.
 
-EOP
+QED