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bionication
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bionication
I have a question that involves taking the roots of a number.
\(\sqrt{64}\) = 8

However, why can't it equal -8. For example:
x = \(\sqrt{64}\)
(x)^2 = \(\sqrt{64}\)^2
\(x^2-64=0\)
\((x-8)(x+8)=0\)
\(x= +/-8\)

Thanks in advance for your help!

When the GMAT provides the square root sign for an even root, such as a square root, fourth root, etc. then the only accepted answer is the positive root. That is:

\(\sqrt{9} = 3\), NOT +3 or -3;
\(\sqrt[4]{16} = 2\), NOT +2 or -2;

Notice that in contrast, the equation \(x^2 = 9\) has TWO solutions, +3 and -3. Because \(x^2 = 9\) means that \(x =-\sqrt{9}=-3\) or \(x=\sqrt{9}=3\).

Theory on Number Properties: math-number-theory-88376.html
Tips on Numper Properties: number-properties-tips-and-hints-174996.html

All DS Number Properties Problems to practice: search.php?search_id=tag&tag_id=38
All PS Number Properties Problems to practice: search.php?search_id=tag&tag_id=59

Hope it helps.
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awesome explanation...Thanks Bunuel...
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Thanks for the explanation, Bunuel. Odd roots would function differently, as you could take the cube root of -27 or -64. But an even root could never yield a negative outcome, as anything squared would become positive. It's much clearer now.
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I know this is an old post, but I thought I'd mention that I recently wrote an article on our GMAT blog about this issue!

https://www.manhattanprep.com/gmat/blog ... -the-gmat/

There are even some practice problems to try out.
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