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What is the square root of -81?

I know I can't be solved but it has an answer

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Technically you can find the root of a negative number but it is complex algebra and you obviously don't need to know that formula but I will include the link.

The answer normally for these questions would be none, no answer or maybe undefinable. (full disclosure I had to ask my mom who teaches high school math what she would require on her tests). So for your purposes, the answer is none or no answer.

The link to find the technically and mathematically "right" answer includes imaginary numbers etc.

http://mathforum.org/library/drmath/view/52613.html

UPDATED - i was told to say "non real number"

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I believe it would be 9i, i being the square root of negative 1.

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Yeah. That's what I was tryin to say. :)

My head hurts. I tried to get the answer from wikipedia. 8/
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You were faster with the complex algebra answer. I tried to explain the details.... Gotta love math right?
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Haha thanks, yeah i just so happen to be good at it so i dont mind it :)
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-9

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=81
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-9 squared is +81.
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A square root is a number which, when multiplied by itself, equals the original number. As 9 x 9 = 81 and -9 x -9 = 81, the answer is plus or minus nine.
9.

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Your answer would be correct if the question was -(square root of 81) not square root of -81. Negative numbers don't have square roots. The complex algebra answer is -9i. The basic algebra answer is none.
You can square negative integers but not find square roots.
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okay if you say so. genius
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ow sorry for me, I'll turn back time so I can go back to my pre-algebra, see you
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sotelo...-9 squared is positive 81, sorry.
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From wiki: (although the actual equations didn't copy)

The square of any positive or negative number is positive, and the square of 0 is 0. Therefore, no negative number can have a real square root. However, it is possible to work with a more inclusive set of numbers, called the complex numbers, that does contain solutions to the square root of a negative number. This is done by introducing a new number, denoted by i (sometimes j, especially in the context of electricity where "i" traditionally represents electric current) and called the imaginary unit, which is defined such that i2 = ?1. Using this notation, we can think of i as the square root of ?1, but notice that we also have (?i)2 = i2 = ?1 and so ?i is also a square root of ?1. By convention, the principal square root of ?1 is i, or more generally, if x is any positive number, then the principal square root of ?x is

The right side (as well as its negative) is indeed a square root of ?x, since

(Whatever THAT means.)

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A square root number cant be negative, so outside of the square root would be an "I" representing a -1.

Once you find the square root, you multiple the answer my -1 or i.

-81 = (-1)* -/9 or 9i

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-9