Applications
If you are interested in why these concepts are so widely used, read the article through the following link (You may have to copy and paste the link into an address bar):
https://www.quora.com/If-complex-numbers-are-imaginary-then-what-is-their-significance-in-the-real-world-Why-should-we-study-complex-numbers
One of the main reasons for the study of complex numbers is for using the Residue Theorem, which is essentially a method for computing the area, or residue, of unbounded functions around the point(s) at which the function is unbounded. Differentiation plays a key role in establishing the criterion for applying the Residue Theorem, but that's hardly a topic for a Monday!
Phew, hope you enjoyed the read!