Question:medium

If C is the positively oriented circle represented by \( |z|=2 \), then \( \int_C \frac{e^{2z}}{z-4} dz \) is:

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When evaluating a contour integral, the very first step is to locate the singularities (poles) of the integrand and check if they are inside, outside, or on the contour. If all singularities are outside, the integral is zero by Cauchy's Integral Theorem.
Updated On: Feb 10, 2026
  • \( \frac{2\pi i}{3} \)
  • \( \pi i \)
  • \( \frac{4\pi i}{3} \)
  • 0
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The Correct Option is D

Solution and Explanation

We need to evaluate the following contour integral:

\[ \int_C \frac{e^{2z}}{z-4} \, dz \]

where \( C \) is a circle defined by \( |z| = 2 \), oriented counterclockwise. Let's analyze it.

Step 1: Identify the Integral's Structure

The integrand is structured as \( \frac{f(z)}{z - a} \), with \( f(z) = e^{2z} \), which is analytic (holomorphic) everywhere. The denominator \( z - 4 \) presents a singularity at \( z = 4 \).

Step 2: Consider Cauchy's Integral Formula

Cauchy's Integral Formula applies if \( f(z) \) is analytic inside and on a closed contour \( C \), and \( a \) is inside \( C \):

\[ \int_C \frac{f(z)}{z - a} \, dz = 2\pi i \, f(a) \]

However, in this problem, the singularity \( z = 4 \) is located outside the contour \( C \) because \( |4| > 2 \) and \( C \) is the circle \( |z| = 2 \). Thus, Cauchy's formula is not directly applicable here.

Step 3: Conclusion by Residue Theorem

Since the singularity lies outside the contour, the residue at \( z = 4 \) does not influence the integral's value. Applying the residue theorem (or Cauchy's theorem) leads to:

\[ \int_C \frac{e^{2z}}{z-4} \, dz = 0 \]

Final Answer:

The contour integral evaluates to:

\[ \boxed{0} \]

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