Note that diff(f) is alsoa symbolic function, so you can use find_root on it as well, and specify an interval, e.g.
find_root(diff(f), 0, 1)

Note that diff(f) is alsoa also a symbolic function, so you can use find_root on it as well, and specify an interval, e.g.
find_root(diff(f), 0, 1)