Purely Imaginary Number

A complex number z is said to be purely imaginary if it has no real part, i.e., R[z]=0. The term is often used in preference to the simpler "imaginary" in situations where z can in general assume complex values with nonzero real parts, but in a particular case of interest, the real part is identically zero.

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Weisstein, Eric W. "Purely Imaginary Number." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/PurelyImaginaryNumber.html

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