The Complex Numbers
Numbers of the form z = x + yi, where x and y are real and i = - 1art/square-root-of-negative-1.gifthe square root of negative 1, such as 8 + 7 i (or 8 + 7 - 1art/square-root-of-negative-1.gif times the square root of negative 1), are called complex numbers; x is called the real part of z and yi the imaginary part. The real numbers are thus complex numbers with y = 0; e.g., the real number 4 can be expressed as the complex number 4 + 0 i. The complex numbers are in a one-to-one correspondence with the points of a plane, with one axis defining the real parts of the numbers and one axis defining the imaginary parts. Mathematicians have extended this concept even further, as in quaternions.
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