(Solved): f(x) is continous on (-infinty,infinity) and has critical numbers at x=a,b,c and d. use the sign cha ...

$f(x)$ is continuous on $(??,?)$ and has critical numbers at $x=a,b,c$, and d. Use the sign chart for $f^{?}(x)$ to determine whether $f$ has a local maximum, a local minimum, or neither at each critical number. Does $f(x)$ have a local minimum, a local maximum, or no local extremum at $x=a$ ? Choose the correct answer below. A. a local minimum B. a local maximum C. no local extremum