If a nonconstant solution $y(t)$ to the autonomous DE $y' = f(y)$ has an inflection point at $t=a$, what must be true at $t=a$?
I am given three options: when $f(y) = 0$, when $f'(y) = 0$, and when $f''(y) = 0$.
Am I right in thinking that it must be $f'(y) = 0$ since to have an inflection point, we need $y'' = 0$ and $y'' = f'(y)$?