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x^6 - y^6 = 0

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Source: — Data Sufficiency |
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Re: x^6 - y^6 = 0

by logitech » Fri Nov 07, 2008 10:21 am
teekayy wrote:If x^6 - y^6 = 0, what is the value of x^3 - y^3?

(1) x is positive
(2) y is greater than 1

answer: C
x^6 - y^6 = (x^3 - y^3?) (x^3 + y^3) = 0

Either x^3 - y^3 = 0 , which means X=Y

x^3 + y^3 = 0, which means X = -Y

(1) x is positive - Insuf, we don't know anything about Y
(2) y is greater than 1 -Insuf we dont know anything about X

1+2) x and y positive

so x^3 - y^3 = 0

C
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by Bidisha800 » Sat Nov 08, 2008 11:29 pm
(x^3-y^3)*(x^3+y^3)=0

therefore either (x^3-y^3)=0 or (x^3+y^3)=0 or both =0

(A) and (B) are alone insufficient.


Combining (A) and (B) we get : x is positive and y>1, (x^3+y^3) >0
Therefore (x^3-y^3) must be =0
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