The second imaginary number

[Kaj]

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How important is the second natural number in mathematics? I am of course talking about the number whose square is 4.

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Not very important as it is just -(h^2).

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-2(h^2) actually.

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That would be an i in your equation, not an h.

[Siegmund]

I would guess that, if you asked a mathematician to name "the second imaginary number," he would say "j" (for generalizing the complex numbers to the quaternions, just as i generalizes the reals to the complex numbers.)

But whichever definition you use, it'll be considerably less important-sounding than the first.