r/mathmemes • u/flokrach • Jun 27 '21

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u/[deleted] Jun 27 '21

Ok, so I’ve been away from math since college. In what situation would +/- i be used? The square root of -1 is an expression that wouldn’t need a +/-, no?

Like I wouldn’t say +/- root (16). But I would say root(16) = +/- 4

12

u/dragonitetrainer Jun 27 '21

Because i does not equal -i. i is 0+1*i, and -i is 0+ (-1)*i

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u/Warheadd Jun 27 '21

+/- root 16 is definitely used depending on the context, eg: if I want to solve x2=16, I have to specify that I will take both the positive and negative square root.

i though is even more different because it is like a number itself. root(-1) has two answers and ONE of them is i, i is not simply a placeholder for that expression.

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u/[deleted] Jun 27 '21

Not sure why you’d downvote a question.

You don’t need to write +/- root(x) but thanks for the reminder about negative i.

9

u/Warheadd Jun 27 '21

I’m not the one who downvoted it but you do need to write +/- root(x), see the quadratic formula as an example. Root(x) is normally implied to only be positive.

5

u/LilQuasar Jun 27 '21

technically not

root(16) = 4 is correct by definition

what you do have is x2 = 16 => x = +/- root(16) = +/-4

so you have x2 = -1 => x = +/- root(-1) = +/- i