Some time ago I published an article on how to calculate Discrete Fourier Transforms in Excel. It proved to be a very popular tutorial. However, I got asked questions as to why is the complex number formula for DFTs used in Excel. Fourier analysis is primarily about the use of trigonometric functions, so why do we have imaginary numbers in this formula? This paper is a gentle introduction to this topic for all those who have not studied mathematics as their primary subject.
To read the tutorial go here, and to check the spreadsheet demonstrating how all the calculations are executed, click here.