challenge: What is the goal of the minimization problem illustrated in the figure related to Fenchel's duality theorem?
  
  A. To vary x such that the horizontal distance between the curves is as large as possible
  B. To vary x such that the vertical distance between the convex and concave curves at x is as small as possible
  C. To find the point where the curves intersect
  D. To maximize the vertical distance between the convex and concave curves at x
  Answer: 