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Although most of us do not use imaginary numbers in our daily life, in engineering and physics they are in fact used to represent physical quantities, just as we would use a real number to represent something physical like the length of a stick or the distance from your house to your school.
In general, an imaginary number is used in combination with a real number to form something called a complex number, a+bi where a is the real part (real number), and bi is the imaginary part (real number times the imaginary unit i). This number is useful for representing two dimensional variables where both dimensions are physically significant. Think of it as the difference between a variable for the length of a stick (one dimension only), and a variable for the size of a photograph (2 dimensions, one for length, one for width). For the photograph, we could use a complex number to describe it where the real part would quantify one dimension, and the imaginary part would quantify the other.
In electrical engineering, for example, alternating current is often represented by a complex number. This current requires two dimensions to represent it because both the intensity and the timing of the current is important. If instead it were a DC current, where the current was totally constant with no timing component, only one dimension is required and we don't need a complex number so a real number is sufficient. The two key points to remember are that the imaginary part of the complex number represents something physical, unlike it's name implies, and that the imaginary number is used in complex numbers to represent a second dimension.
Remember, a purely imaginary voltage in an AC circuit will shock you as badly as a real voltage - that's proof enough of it's physical existence. I'll put a link in the link area to a great interactive site (it's actually my site but for it's educational purposes only) that explains the imaginary number utility more visually with animations.
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What are the real numbers that is not a whole number?
Real numbers are all numbers which do not contain "i", when "i" represents the square root of -1. All numbers which do contain "i" are "imaginary numbers" and are not real numbers. This means that all numbers you'd ordinarily use are real numbers - all the counting numbers (integers) and all decimals are real numbers. So in answer to your question, all the real numbers that are not whole numbers are all the decimal numbers - including irrational decimals such as pi.
Jobs that require the use of imaginary numbers?
Physics (e.g., quantum mechanics, relativity, other subfields) makes use of imaginary numbers. "Complex analysis" (i.e., calculus that includes imaginary numbers) can also be used to evaluate difficult integrals and to perform other mathematical tricks. Engineering, especially Electrical Engineering makes use of complex and imaginary numbers to simplify analysis of some circuits and waveforms.
Where did complex and imaginary numbers come from?
The 16th century Italian mathematician, Gerolamo Cardano was the first to use imaginary and complex numbers in his work on cubic equations.
When do you use multiplication of negative numbers in real life?
It is possible to live a long and productive life without ever multiplying a negative number outside of a classroom.
Why do you need imaginary numbers?
because somtimes there isn't an answer to every equation like what's the square root of -16.... there is no answer so we would just use an imaginary number which is i.It turns out that these are important in a practical sense. Imaginary numbers turn up all the time in quantum mechanics and certain types of electronic circuits as well.
