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# x^6 - y^6 = 0 (x ^3) ^2 - (y ^3) ^2 = 0 (x ^3- y ^3)(x ^3+ y

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Senior Manager
Joined: 08 Jan 2009
Posts: 317
x^6 - y^6 = 0 (x ^3) ^2 - (y ^3) ^2 = 0 (x ^3- y ^3)(x ^3+ y [#permalink]

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13 Jun 2009, 18:57
00:00

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions

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x^6 - y^6 = 0

(x ^3) ^2 - (y ^3) ^2 = 0
(x ^3- y ^3)(x ^3+ y ^3) = 0

so either one has to be equal to zero

1. xy > 0
x and y are +ve then (x ^3- y ^3) has to be zero because (x ^3+ y ^3) = +ve
x and y are -ve then (x ^3- y ^3) has to be zero because (x ^3+ y ^3) = -ve.

Sufcicient.

2. x = 2
( 8-y^3) ( 8+y^3) = 0
if y is +ve then ( 8+y^3) = +ve and ( 8-y^3) = 0
if y is -ve then ( 8-y^3) = +ve and ( 8+y^3) = 0

Insufficient.

So IMO is A.

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Manager
Joined: 28 Jan 2004
Posts: 201
Location: India

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14 Jun 2009, 22:49
A
Same explanation as tkarthi4u

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If you would like to discuss this question please re-post it in the respective forum. Thank you!

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Re: x-cubed minus y-cubed   [#permalink] 14 Jun 2009, 22:49
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