This video shows how to convert from a sine wave to a cosine wave. This trick is used when writing phasors in electrical engineering and electromagnetics.
I am teaching using the Fawwaz T. Ulaby textbook as a reference. This is covered in chapter 1-7 of Fundamentals of Applied Electromagnetics, 8th edition.
For more information about Fundamentals of Applied Electromagnetics by Ulaby please visit this website: https://em8e.eecs.umich.edu/