1

Goal: Let $\gamma$ be the unit circle. Then I aim to compute

$$ \int_{|z|=1} {e^z \over z}\ dz = \int_{\gamma} {e^z \over z}\ dz $$

Attempt:

  1. Consider that $\gamma$ is a closed curve.

  2. Let $a = 0$. Then $e^a = 1$. Furthermore, $\gamma \cap \{a\} = \emptyset$.

  3. We have by another theorem if $f$ is analytic inside some disk $\Delta$, and if $\gamma$ is a closed curve in $\Delta$ that does not intersect some point $a \in \Delta$, then

    $$ f(a) \cdot n(\gamma, a) = {1 \over 2 \pi i} \int_\gamma {f(z) \over z-a}\ dz $$

  4. Then combining the facts from above with the fact that $e^z$ is analytic on the whole plane (hence analytic inside any disk that contains the unit circle), we have that

$$ \int_\gamma {e^z \over z - a}\ dz = f(a) n(\gamma, a) = n(\gamma, 0) $$

Question: Is my reasoning correct? Is there an easy way we compute the exact integer value of $n(\gamma,0)$?

user1770201
  • 5,361
  • 6
  • 44
  • 80

1 Answers1

1

Hint: do it explicitly for the function $f(z) = 1$.

Robert Israel
  • 470,583