It's true when you let go to 0.
Hello. I am attempting to evaluate
using a contour integral on the function . My contour will be a "keyhole contour" suggested by Wikipedia: Methods of contour integration - Wikipedia, the free encyclopedia.
I tried to follow their example, but could not understand this:
Why is it permissible to substitute ? Is it perhaps because they have taken , so this line gets close to the position?
I would appreciate any clarification on this example.