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electrical engineers and quantum mechanics use them.
Complex numbers are theoretically interesting; they help us better understand the real numbers in some cases.They also have some very practical applications, including: * Electrical circuits - in AC, things like resistance, current, and voltage acquire a phase angle, thus becoming complex numbers. * Quantum mechanics - the probability amplitude is described with a complex number. As a result, complex numbers basically permeate all of quantum mechanics.
Among other things, complex numbers play an important role:* In electrical circuits - quantities in AC circuits are described by complex numbers. * In quantum mechanics - the "probability amplitude" is an important concept in quantum mechanics, and it is described by a complex number. * In art - for example, the Mandelbrot set is based on calculations with complex numbers.
One operation that is used a lot in quantum mechanics is taking the absolute value of the square of a complex number. This is equivalent to multiplying the complex number by its complex conjugate - and doing this is simpler in practice.
The real numbers together with the imaginary numbers form a sort of vector. What these complex numbers (complex means the combination of real and imaginary numbers) represent depends on the specific situation. Just as there are situations where it doesn't make sense to use negative numbers, or fractional numbers, in many common situations it doesn't make sense to use complex numbers. In an electrical circuit (specifically, AC), the real numbers might represent resistance, while the imaginary number represent reactance - and voltages and currents are also represented by complex numbers, with the angle of the complex number representing how much one quantity is ahead or behind another quantity (the "phase angle"). In quantum mechanics, the complex numbers might not represent anything (perhaps they don't, I am not sure...), but they are useful for calculations.