Answer the following questions about local extrema of differentiable functions.
a. (i) Define a stationary point of a real-valued function f.
b. (ii) State the conditions on f′′(c) that decide whether a stationary point x=c is a local maximum or a local minimum.
c. (iii) For the function g(x)=x4, show that x=0 is a stationary point where g′′(0)=0. Explain why the nature of this point cannot be concluded directly from g′′(0) and state what you can say about x=0 for this function.