# How is complex analysis relevant to other areas of mathematics?

I'm going to do a math PhD next year. My main interests in mathematics are composition algebra, algebraic topology, and group theory.

Now I have the opportunity to take a one-semester course in complex analysis, but I am not sure if it is relevant to my research interests.

My understanding of complex analysis is that it is mostly about Laurent series, Cauchy's integral theorem, residue theorem, and evaluating weird-looking real integrals using these techniques. But I fail to see its connection to algebra.

I am sure that it is a beautiful theory and that it is also an important set of tools for applied mathematicians and engineers, but is there anything useful I can take from complex analysis as an algebraist?

• It's crucial in number theory .... – Angina Seng Jul 10 '17 at 6:44
• @Lord Shark the Unknown Analytic Number Theory... – Pixel Jul 10 '17 at 6:48
• Consider $(-1)^x$ where $x>0$ is a real number. – Wuestenfux Jul 10 '17 at 6:50
• You fail to see connections, I fail to see boundaries. Mathematics is one science, personal limitations and the (non-scientific) conditions of mathematical research enforce specialization. That's all. The fundamental theorem of algebra: every non-constant polynomial has a complex zero. One line proof: otherwise, $1/p(z)$ would be a bounded, analytic function. – Professor Vector Jul 10 '17 at 6:52
• Complex analysis is black magic. The proof of FTA (mentioned in above comment) becomes trivial thanks to a certain Liouville's theorem in complex analysis. There is "Complex analysis in number theory" by A. Karatsuba to further elaborate on the usefulness of complex analysis. As you may already guess, lots to do with prime number theory and the zeta function. – Alvin Lepik Jul 10 '17 at 7:01