Reduction of Order Theorem

Let $y_1$ be a (not identically zero) solution to $y^{\prime \prime }+p(t)y^{\prime }+q(t)y=0$ for $t>0$

$$y_2(t)=y_1(t)\int \frac{e^{-\int p(t)dt}}{y_1^2(t)}dt$$