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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,yR}

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,yR, 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) | xR}C. It is also common to use the term purely imaginary for any complex number of the form (0,y), where yR. 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.

It is often significantly easier to perform arithmetic operations on complex numbers when written in this form, as we illustrate in the next section.

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This page titled 2.1: Definition of Complex Numbers is shared under a not declared license and was authored, remixed, and/or curated by Isaiah Lankham, Bruno Nachtergaele, & Anne Schilling.

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