Complex Numbers
The most selfish kind of numbers: for them its all about ' i '.
These little guys that drive undergrads wild with anticipation are little more than extentions upon real numbers. Real numbers, like most engineering students, hook up with imaginary counterparts to form the complex plane.
Every complex number is denoted a + b*i , where a represents the real portion and b*i is imaginary portion with i= $ sqrt(-1) $. It then follows that:
$ i^2 = -1 $
$ i^3 = -i $
$ i^4 = 1 $