\newsectionNoPB
\subsection{Linear Differential Equations}
\compactdef{Linear differential equation of order $k$}
$y^{(k)} + a_{k - 1}y^{(k - 1)} + \ldots + a_1 y' + a_0 y = b$, with $a_i$ and $b$ functions in $x$. 
If $b(x) = 0 \smallhspace \forall x$, \bi{homogeneous}, else \bi{inhomogeneous}
