>>Quite right, R is a subset of C, C is form a +/- bi where a,b are real, i=sqrt(-1), and b=0 for R (real), etc.
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>The definition for i: i**2=-1. Because sqrt is not defined on negative numbers.
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No argument on that. But i=sqrt(-1) is what is (at least when I taught math) commonly used as a tool to explain to 'non-math' people what the imaginary part of a non-real quadratic solution is...