32. If a trapezoidal sum underapproximates \[ \int_a^b f(x)\, dx, \] and a right Riemann sum overapproximates \[ \int_a^b f(x)\, dx, \] which of the following could be the graph of \( y = f(x) \)?






Answer is: option3

(C)

Solution:

Trapezoidal Rule Behavior:

  1. Trapezoid sums underapproximate when the function is concave down (∩ shape).
  2. Trapezoid sums overapproximate when the function is concave up (∪ shape).

Right Riemann Sum Behavior:

  1. Right Riemann sums overapproximate when the function is increasing.
  2. Right Riemann sums underapproximate when the function is decreasing.

So we need a function that is:

  1. Concave down
  2. Increasing
  1. (A) Decreasing and concave down → Right Riemann sum would underapproximate. ❌
  2. (B) Increasing and concave up → Trapezoid would overapproximate. ❌
  3. (C) Increasing and concave down → ✔ This matches both clues.
  4. (D) Decreasing and concave down → Right Riemann underapproximates. ❌

Option C

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