Let $f$ be a function with $f(x)>0$ for all $x .$ Set $g=1 / f$
(a) If $f$ is increasing in an interval around $x_{0},$ what about $g ?$
(b) If $f$ has a local maximum at $x_{1},$ what about $g$ ?
(c) If $f$ is concave down at $x_{2},$ what about $g$ ?