Fix typos

ch-first-order-ode.tex

@@ -3208,16 +3208,16 @@ \subsection{Exercises}
 $\bigl( 2y + \frac{y^2}{x} \bigr) \, dx + ( 2y+x )\, dy = 0$
 \end{exercise}
 \exsol{%
-a) Integrating factor is $y$, the equation becomes $dx + 3y^2\,dx = 0$.
+a) Integrating factor is $y$, the equation becomes $dx + 3y^2\,dy = 0$.
 \qquad
-b) Integrating factor is $e^x$, the equation becomes $e^x \, dx - e^{-y}\,dx
+b) Integrating factor is $e^x$, the equation becomes $e^x \, dx - e^{-y}\,dy
 = 0$.
 \qquad
 c) Integrating factor is $y^2$, the equation becomes $(\cos(x)+y)\, dx +
 x\,dy = 0$.
 \qquad
 d) Integrating factor is $x$, the equation becomes $( 2xy+y^2 )\, dx +
-(x^2+2xy)\,dx = 0$.
+(x^2+2xy)\,dy = 0$.
 }
 
 \begin{exercise}

diffyqs.tex

@@ -141,7 +141,7 @@
 %PRINT
 %\medskip
 %\noindent
-%Amazon KDP edition\\
+%Amazon KDP / Createspace edition\\
 %ISBN-13: 978-1541329058
 
 %PRINT