Let f be a function with a stationary point at x=c such that f′(c)=0 and f′′(c)=0. Which of the following statements is correct regarding the use of the second derivative test at x=c?
a) f(c) is a local minimum.
b) It gives no conclusion; further investigation is required.
c) x=c is a point of inflection.
d) x=c is not a stationary point.