Let f be a twice-differentiable function that is concave up on the closed interval [2,6]. The interval is divided into n equal subintervals, and both the midpoint and trapezoidal approximations to ∫26f(x)dx are computed. Which of the following correctly describes the relative sizes of these two approximations and the exact value of the integral?
a) Trapezoidal approximation < exact value < midpoint approximation
b) Exact value < midpoint approximation < trapezoidal approximation
c) Midpoint approximation < exact value < trapezoidal approximation
d) Both the midpoint and trapezoidal approximations exceed the exact value