In my calc $2$ textbook there is an initial-value problem that requires the use of separation of variables.

> 
> The differential equation is $\frac{dy}{dx} = \left(2x+3\right)\left(y^2-4\right)$ with initial value $y(0)=1$.
> 
> 
> 

In the list of steps to take to solve this equation using separation of variables, the very first step is "Check for any values of $y$ that make $g(y) = 0$. These correspond to constant solutions". When I solve $g(y)=0$ I get $g(y) = \pm 2$, but I don't really understand how these values are used to solve this equation?