(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

This isn't a homework problem but just a fundamental concept that my entire complex analysis course is based on.

The set D = ℂ \ non-positive real axis. Why is it considered open and connected (domain)?

2. Relevant equations

3. The attempt at a solution

When it says non-positive real axis, is the origin included? I can see why D is connected. But why is it considered open? The set is open when it contains all of its boundaries. But the set D clearly does not contain any point on the non-positive real axis.

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# Homework Help: Why is this set Open and Connected?

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