fix typo

uni/mmme/1026_maths_for_engineering/calculus.md

@@ -765,7 +765,7 @@ Rearrange to get
 
 \begin{align*}
 \int\! \frac1y \,\mathrm dy &= \int\! k \mathrm dx + c \\
-\ln y &= kx + c
+\ln y &= kx + c \\
 y &= e^{kx + c} = e^ce^{kx} \\
   &= Ae^{kx}
 \end{align*}