Let p=\int_{a}^{b}f(x)\,dx and q=\int_{a}^{b}|f(x)|\,dx. If f(x)=e^{-x}, then which one of the following is correct?

  1. A. p=2q
  2. B. p=-q
  3. C. 4p=q
  4. D. p=q

Correct Answer: D. p=q

Explanation

For all real values of x, the exponential function e^{-x} is strictly positive. Therefore, |f(x)| = |e^{-x}| = e^{-x} = f(x). Since the integrand is identical, their definite integrals over [a, b] are exactly equal, meaning p = q.

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