This document discusses the history and properties of complex numbers. It begins by outlining the key topics to be covered: history, number systems, complex numbers themselves, and operations. It then provides details on who originally introduced complex numbers and the symbols used. Complex numbers combine real and imaginary numbers and can be expressed as a + bi, where a is the real part and b is the imaginary part. The document also describes how complex numbers extend the number line to the complex plane and defines the basic operations of addition, subtraction, multiplication, and division of complex numbers.