A function f is increasing and concave up on the interval [2,8]. Four equal-width subintervals are used to create three different Riemann sums:
• one that samples at the left endpoints,
• one that samples at the right endpoints, and
• one that samples at the halfway point of each subinterval.
Which ordering of the three sums must be true?
a) Left-endpoint sum < Right-endpoint sum < Halfway-point sum
b) Right-endpoint sum < Left-endpoint sum < Halfway-point sum
c) Left-endpoint sum < Halfway-point sum < Right-endpoint sum
d) Halfway-point sum < Left-endpoint sum < Right-endpoint sum