Absolute value - Wikipedia
https://en.wikipedia.org/wiki/Absolute_valueThe definition of absolute value given for real numbers above can be extended to any ordered ring. That is, if a is an element of an ordered ring R, then the absolute value of a, denoted by |a|, is defined to be: where −a is the additive inverse of a, 0 is the additive identity, and < and ≥ have the usual meaning with respect to the ordering in the ring.
Complex number - Wikipedia
https://en.wikipedia.org/wiki/Complex_numberComplex numbers have a similar definition of equality to real numbers; two complex numbers a1 + b1i and a2 + b2i are equal if and only if both their real and imaginary parts are equal, that is, if a1 = a2 and b1 = b2. Nonzero complex numbers written in polar form are equal if and only if they have the same magnitude and their arguments differ by an integer multiple of 2π.