2.1: Definition of Complex Numbers
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We begin with the following definition.
Definition 2.1.1: complex numbers
The set of complex numbers C is defined as
C={(x,y) | x,y∈R}
Given a complex number z=(x,y), we call RealPart(z)=x the real part of z and ImaginaryPart(z)=y the imaginary part of z.
In other words, we are defining a new collection of numbers z by taking every possible ordered pair (x,y) of real numbers x,y∈R, and x is called the real part of the ordered pair (x,y) in order to imply that the set R of real numbers should be identified with the subset {(x,0) | x∈R}⊂C. It is also common to use the term purely imaginary for any complex number of the form (0,y), where y∈R. In particular, the complex number i=(0,1) is special, and it is called the imaginary unit. (The use of i is standard when denoting this complex number, though j is sometimes used if i means something else. E.g., i is used to denote electric current in Electrical Engineering.)
Note that if we write 1=(1,0), then we can express z=(x,y) in C as
z=(x,y)=x(1,0)+y(0,1)=x1+yi=x+yi.
Contributors
- Isaiah Lankham, Mathematics Department at UC Davis
- Bruno Nachtergaele, Mathematics Department at UC Davis
- Anne Schilling, Mathematics Department at UC Davis
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