Let us consider the equation
,
and its associated homogeneous equation
The following basic results hold:
is also solution of the equation (H). This solution is called
a linear combination of the functions ;
where are arbitrary constants and
are n solutions of the equation (H)
such that,
In this case, we will say that are linearly
independent. The function
is called the
Wronskian of
. We have
Therefore, , for some
, if and only if,
for every x;
where are arbitrary constants,
are linearly independents solutions of the
associated homogeneous equation (H), and
is a particular
solution of (NH).