Abel's identity

for

$$y^{\prime \prime }+p(t)y^{\prime }+q(t)y=0$$ $$W(t)=W(y_1,\dots ,y_n)(t)=c{e}^{-\int p(t)dt}$$

where $W$ is Wronskian determinant and $c$ is a constant by $W$ at convenient point.