3. Let f(x)=x²-4x³ +21. Determine the following features of f: domain, intercepts,

intervals where f is increasing or decreasing, relative extrema, intervals where f is

concave upward or concave downward, inflection points. Use all those features to

sketch the graph of f. Hint: you can skip the step of finding z-intercept and still

connect the dots to the sketch the curve.