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Finding values .... !!!

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by AIM GMAT » Tue Jan 25, 2011 11:17 pm
If x^2 + y^2 = 29 , what is the value of (x - y)^2 ?

1] xy = 10
2] x = 5


I was confused with the given OA , but actually while typing this question i realised my fault and understood why OA is so .OA after some discussions.
Thanks & Regards,
AIM GMAT
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Source: — Data Sufficiency |

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by Anurag@Gurome » Tue Jan 25, 2011 11:29 pm
AIM GMAT wrote:If x² + y² = 29 , what is the value of (x - y)² ?

1] xy = 10
2] x = 5
(x - y)² = (x² + 2xy + y²) = (x² + y²) + 2xy = 29 + 2xy
If we know the value of xy, we can determine the value of (x - y)².

Statement 1: Sufficient

Statement 2: x = 5
Implies, x² = 25
Hence, y² = (29 - 25) = 4 => y = ±2
Hence, xy = ±10 => 2xy = ±20

Not sufficient

The correct answer is A.
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by gmatmachoman » Tue Jan 25, 2011 11:30 pm
AIM GMAT wrote:If x^2 + y^2 = 29 , what is the value of (x - y)^2 ?

1] xy = 10
2] x = 5


I was confused with the given OA , but actually while typing this question i realised my fault and understood why OA is so .OA after some discussions.
(x - y)^2 = x^2 +Y^2 -2XY

st 1:

use the given value & substitute that.... Sufficient

St 2:

Using this u can't get "distinct" value of Yas Y can be postive or negative

Pick A
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by AIM GMAT » Tue Jan 25, 2011 11:55 pm
Thanks Anurag and gmatmachoman for the explanations , initially i didnt realise why st 2 cant give exact value .
Thanks & Regards,
AIM GMAT
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