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# (x-y)2=?

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Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6806
GMAT 1: 760 Q51 V42
GPA: 3.82

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09 Feb 2017, 04:26
00:00

Difficulty:

45% (medium)

Question Stats:

64% (01:13) correct 36% (01:24) wrong based on 58 sessions

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$$(x-y)^2=?$$

$$1) x^2+y^2=8$$
$$2) (x+y)^2=4xy$$

_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $149 for 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Senior Manager Joined: 19 Apr 2016 Posts: 274 Location: India GMAT 1: 570 Q48 V22 GMAT 2: 640 Q49 V28 GPA: 3.5 WE: Web Development (Computer Software) (x-y)2=? [#permalink] ### Show Tags 09 Feb 2017, 04:34 MathRevolution wrote: $$(x-y)^2=?$$ $$1) x^2+y^2=8$$ $$2) (x+y)^2=4xy$$ $$(x-y)^2= x^2+y^2-2xy$$ St I $$x^2+y^2=8$$ =>$$(x-y)^2= 8-2xy$$ ----------Insufficient St II $$(x+y)^2=4xy$$ => $$x^2+y^2 + 2xy=4xy$$ => $$x^2+y^2 =2xy$$ Therefore we have, $$(x-y)^2= x^2+y^2-2xy$$ =>$$(x-y)^2= 2xy-2xy$$ =0 ----------Sufficient Hence Option B is correct. Hit Kudos if you liked it Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 6806 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: (x-y)2=? [#permalink] ### Show Tags 12 Feb 2017, 17:20 ==> If you modify the original condition and the question, from $$(x-y)^2=x^2+y^2-2xy=x^2+y^2+2xy-4xy= (x+y)^2-4xy$$, con 2) is sufficient. Therefore, the answer is B. Answer: B _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$149 for 3 month Online Course"
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13 Feb 2017, 00:22
MathRevolution wrote:
$$(x-y)^2=?$$

$$1) x^2+y^2=8$$
$$2) (x+y)^2=4xy$$

A--Not suff
B-(x+y)^2 = 4xy
x^2 + y^2 +2xy =4xy
x^2 + y^2 - 2xy = 0
(x-y)^2 = 0
Suff.
hence B
Re: (x-y)2=? &nbs [#permalink] 13 Feb 2017, 00:22
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