Can someone please explain the green text to me?
Maybe I am not reading it right, but that sentence makes no sense to me. "that (2) is an equation For which $xp(x)$ and $x^2q(x)$ " what does this part mean? The next part that follows sys something about being constants. Are they trying to say we should replace equation (2) with $xp(x)$ and $x^2q(x)$ like
$$y''(x) + xp(x)y'(x) + x^2q(x)y(x) = 0 $$ So that
$$y''(x) + p_0y'(x) + q_0y(x) = 0$$
Either case it makes no sense to me at all, especially why they started writing out the $xp(x)$ as a series.