[NumCS] Catch up to current state

semester3/analysis-ii/parts/diffeq/00_intro.tex

@@ -1,6 +1,6 @@
 \subsection{Introduction}
 \shortex $f'(x) = f(x)$ has only solution $f(x) = ae^x$ for any $a \in \R$;
-$f' - a = 0$ has only solution $f(x) = \int_{x_0}^{x} a(t) \smallhspace \dx t$
+$f' - a = 0$ has only solution $f(x) = \int_{x_0}^{x} a(t) \dx t$
 
 \setcounter{all}{6}
 \shorttheorem Let $F: \R^2 \rightarrow \R$ be a differential function of two variables. Let $x_0 \in \R$ and $y_0 \in \R^2$.