Complex number
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A complex number is a number. It only sounds complex, but really is not. With algebra, you can do addition, subtraction, multiplication, and division. Using negative numbers, it is possible to find the x in the equation a + x = b for all possible values of a and b.
With multiplication and division, there is a problem. There is no (normal) number, that gives you -1, when you multiply it by itself. In other words, -1 (or any other negative number) has no square root. To solve this problem, mathematicians introduced an imaginary number called i. That imaginary number will give -1 when you multiply it by itself.
A complex number can now be written as 
, where a is called the real part of the number, and b is called the imaginary part. Usually, the complex number is written as (a,b). Both a and b are real numbers.
A real number can simply be written as 
or (a,0).
With complex numbers it is possible to do all the four basic calculations as defined in algebra, but also more complicated calculations.
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