In Problem, complete the following.

(a) Find the derivative of each function and check your work by graphing both your calculated derivative and the numerical derivative of the function.

(b) Use your graph of the derivative to find points where the original function has horizontal tangent lines.

(c) Use a graphing calculator to graph the function and indicate the points found in part (b) on the graph.

f (x) = (x² - 14x + 49)(2x + 1)