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 Post subject: GRE Algebra (Select One or More)
PostPosted: Sat Feb 25, 2012 4:05 pm 
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Joined: Sun May 30, 2010 3:15 am
Posts: 424
If 20 – √x = 11, then what are possible values of x?

-81, -9, 3, 9, 81

The correct answer is 81.

Let's solve the equation 20 – √x = 11 by combining and rearranging. We get 9 = √x. Squaring both sides results in 81 = x, and this is the only value that x can take on. Thus, only answer 81 will be correct.
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-9 squared is also 81 is it not?


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 Post subject: Re: t.4, s.4, qt.10: equations, radicals
PostPosted: Sat Feb 25, 2012 4:13 pm 
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Joined: Sun May 30, 2010 2:23 am
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Quote:
-9 squared is also 81 is it not?
(-9)² = 81 indeed, but the question is the inverse one.
x = 9, NOT x² = 81.


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