This is a topic I always really loved at university: Imaginary Numbers! Yitzi Litt does a great job at explaining what they are, first by putting them into context of the other types of numbers and then explaining their properties.
This is an animated tutorial on imaginary numbers (the mathematical concept) that I made for a competition. It was made completely with Blender internal, and the music is "enigma Variations" from musopen.org.
I am fourteen years old, and have been using Blender for just over a year.