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If 2x^2 –y^2 = 2xy, then (x+y)^2=

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If 2x^2 –y^2 = 2xy, then (x+y)^2= [#permalink] New post 11 Nov 2010, 21:38
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A
B
C
D
E

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Question Stats:

69% (01:33) correct 30% (02:50) wrong based on 13 sessions
If 2x^2 –y^2 = 2xy, then (x+y)^2=

(A) X^2
(B) 3x^2
(C) 4xy
(D) 2y^2
(E) –y^2
[Reveal] Spoiler: OA

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Re: If 2x^2 –y^2 = 2xy [#permalink] New post 11 Nov 2010, 23:21
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Re: If 2x^2 –y^2 = 2xy [#permalink] New post 12 Nov 2010, 13:46
2x^2 –y^2 = 2xy
2x^2 = 2xy+y^2

3x^2 = x^2 + 2xy+y^2 (adding x^2 on both sides)

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


Answer:- B
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Re: If 2x^2 –y^2 = 2xy [#permalink] New post 12 Nov 2010, 16:30
2x^2-y^2=2xy

(x+y)^2= x^2+2xy+y^2

replace 2xy by 2x^2-y^2 and solve

Answer B.
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Re: If 2x^2 –y^2 = 2xy [#permalink] New post 29 Dec 2010, 12:08
Sarang wrote:
2x^2 –y^2 = 2xy
2x^2 = 2xy+y^2

3x^2 = x^2 + 2xy+y^2 (adding x^2 on both sides)

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


Answer:- B


i didn't understand this pls explain
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Re: If 2x^2 –y^2 = 2xy [#permalink] New post 29 Dec 2010, 12:33
Expert's post
rahul321 wrote:
Sarang wrote:
2x^2 –y^2 = 2xy
2x^2 = 2xy+y^2

3x^2 = x^2 + 2xy+y^2 (adding x^2 on both sides)

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


Answer:- B


i didn't understand this pls explain


Given: 2x^2-y^2=2xy --> rearrange: 2x^2=2xy+y^2 --> add x^2 to both parts of the equation: 2x^2+x^2=x^2+2xy+y^2 --> 3x^2=(x+y)^2.

Hope it's clear.
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Re: If 2x^2 –y^2 = 2xy   [#permalink] 29 Dec 2010, 12:33
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