If x2 + y2 = 1, is x + y = 1? (1) xy = 0 (2) y = 0 : DS Archive
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If x2 + y2 = 1, is x + y = 1? (1) xy = 0 (2) y = 0

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Senior Manager
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If x2 + y2 = 1, is x + y = 1? (1) xy = 0 (2) y = 0 [#permalink]

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01 Dec 2008, 07:50
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If x2 + y2 = 1, is x + y = 1?
(1) xy = 0
(2) y = 0
Manager
Joined: 18 Nov 2008
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01 Dec 2008, 08:40
IMO E

Even combined, x can be either 1 or -1, Insuff
Manager
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01 Dec 2008, 15:07
IMO C

Here is why

x+y = 1
or
(x+y)^2 = 1

x^2 + y^2 + 2xy = 1

1+2xy = 1 ( x^2+y^2 = 1 - given in Q)

or the question is asking is xy =0?

1 - Suff
2- Suff
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Joined: 27 May 2008
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01 Dec 2008, 19:04
IMO E

x2 + y2 = 1 deriving from Q (x+y)^2 = 1+2xy

1) xy = 0; so x+y = +/- 1
2) y=0; x2 = 1; x+y = +/- 1
Senior Manager
Joined: 05 Jun 2008
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02 Dec 2008, 04:05
HG wrote:
IMO C

Here is why

x+y = 1
or
(x+y)^2 = 1

x^2 + y^2 + 2xy = 1

1+2xy = 1 ( x^2+y^2 = 1 - given in Q)

or the question is asking is xy =0?

1 - Suff
2- Suff

Value of X could be -1 or +1 hence E OA isE
Re: DS - Algebra   [#permalink] 02 Dec 2008, 04:05
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