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100 points for $49 worth of Veritas practice GMATs FREE VERITAS PRACTICE GMAT EXAMS Earn 10 Points Per Post Earn 10 Points Per Thanks Earn 10 Points Per Upvote ## equations DS tagged by: Brent@GMATPrepNow ##### This topic has 6 expert replies and 24 member replies Goto page ## equations DS Does (x + a)^2 = y^2? (1) x = y - a (2) x = y + a Legendary Member Joined 26 Apr 2010 Posted: 759 messages Followed by: 3 members Upvotes: 85 got A here it is more clear while using a^2-b^2=(a-b)(a+b) second can be true if a=0 but the value is unknown Legendary Member Joined 22 Jan 2010 Posted: 537 messages Followed by: 1 members Upvotes: 14 A for me as well _________________ GMAT score is equally counted as your GPA and 78 clicks can change you life. ### GMAT/MBA Expert GMAT Instructor Joined 09 Oct 2010 Posted: 1434 messages Followed by: 32 members Upvotes: 59 Hi there, (1) Sufficient: x+a = y therefore (x+a)^2 = y^2 (2) Insufficient: Take a = 0 then x=y hence (x+a)^2 = x^2 = y^2 Take y = a = 1 and x = 2, then 3^2 = (x+a)^2 is different from y^2 = 1 Regards, Fabio. _________________ Fabio Skilnik :: GMATH method creator ( Math for the GMAT) English-speakers :: https://www.gmath.net Portuguese-speakers :: https://www.gmath.com.br Legendary Member Joined 12 Sep 2010 Posted: 752 messages Followed by: 10 members Upvotes: 20 GMAT Score: 700 Night reader wrote: Does (x + a)^2 = y^2? (1) x = y - a (2) x = y + a IMO A what's the OA? Senior | Next Rank: 100 Posts Joined 21 Feb 2010 Posted: 71 messages Upvotes: 3 GMAT Score: 750 IMO A as well as per explanation provided above. whats the OA? Legendary Member Joined 27 Dec 2008 Posted: 1337 messages Followed by: 10 members Upvotes: 127 Test Date: 03/28/11 ashforgmat wrote: IMO A as well as per explanation provided above. whats the OA? good question. without offense - I was not satisfied with the expert's answer at this time too mechanical approach anyways my best try was Quote: Does (x + a)^2 = y^2? (1) x = y - a (2) x = y + a question stem -> |x+a|=|y| OR |x+a|-|y|=0 -> |x+a-y|=0 where i) x+a-y=0, ii) -x-a+y=0 -> both equate x=y-a which is equivalent to -x=a-y st(1) x= y-a is Sufficient st(2) x= y+a is Not Sufficient answer is A. Master | Next Rank: 500 Posts Joined 24 Nov 2009 Posted: 163 messages Followed by: 4 members Upvotes: 13 Test Date: 7/8 Target GMAT Score: 760 GMAT Score: 660 I think the expert reply was short and to the point.....I think you just over analyzed the question. I understand you're trying to see the trick with the absolute values, but it really just leads to the same answer. Maybe the question was just testing to see if you'd over think the question lol! Legendary Member Joined 27 Dec 2008 Posted: 1337 messages Followed by: 10 members Upvotes: 127 Test Date: 03/28/11 chendawg wrote: I think the expert reply was short and to the point.....I think you just over analyzed the question. I understand you're trying to see the trick with the absolute values, but it really just leads to the same answer. Maybe the question was just testing to see if you'd over think the question lol! The problem is testing what it does. OA was A. I pointed out the expert's solution above and followed with my (last) solution to help us see the "if-s" --> (x+a)^2=y^2 is deconstructed into (x+a)(x+a)=y*y where (x+a) can OR can not be equal to y. Because the official answer suggested A, I left this untouched. We had discussion with another fellow in private about this question too. I think the question itself creates an ambiguity. As for over-analysis per DS questions - I'd rather do over- than under- Newbie | Next Rank: 10 Posts Joined 26 Dec 2010 Posted: 2 messages Don't over-analyze. If x = y + a then the stem would become: ((y + a) + a)^2 = y^2 (y + 2a)^2 = y^2 Which only makes sense if a = 0 but is false for any other value. Insufficient. Legendary Member Joined 27 Dec 2008 Posted: 1337 messages Followed by: 10 members Upvotes: 127 Test Date: 03/28/11 hey_deep wrote: Don't over-analyze. If x = y + a then the stem would become: ((y + a) + a)^2 = y^2 (y + 2a)^2 = y^2 Which only makes sense if a = 0 but is false for any other value. Insufficient. is your comment re the 2nd statement? the earlier post was about the 1st statement - I am copying/pasting for clarity purpose: (x+a)^2=y^2 is deconstructed into (x+a)(x+a)=y*y where (x+a) can OR can not be equal to y. When mods are given we should easily spot that difference in values. ... ### GMAT/MBA Expert GMAT Instructor Joined 10 Jan 2011 Posted: 132 messages Followed by: 37 members Upvotes: 68 GMAT Score: 780 Night reader wrote: chendawg wrote: I think the expert reply was short and to the point.....I think you just over analyzed the question. I understand you're trying to see the trick with the absolute values, but it really just leads to the same answer. Maybe the question was just testing to see if you'd over think the question lol! The problem is testing what it does. OA was A. I pointed out the expert's solution above and followed with my (last) solution to help us see the "if-s" --> (x+a)^2=y^2 is deconstructed into (x+a)(x+a)=y*y where (x+a) can OR can not be equal to y. Because the official answer suggested A, I left this untouched. We had discussion with another fellow in private about this question too. I think the question itself creates an ambiguity. As for over-analysis per DS questions - I'd rather do over- than under- I like your point about the deconstruction, as I can see many questions where that would be relevant. However, I think you can tell by looking at this question that it isn't one of them; because the expressions in the Statements are so similar to the expressions in the Prompt, you know that Substitution would be your best option. If you saw something strange like "x I agree that a full analysis of the question is necessary, however, I want to suggest two things to you for greater success on test day: 1) Overanalysis is NOT better than underanalysis. They are both bad. You want to do exactly the right analysis! Remember it's a timed, adaptive test, so you should not be over-analyzing. 2) Analyze the entire question. The Statements often give you a little hint about what kind of question it is. Yes, of course, we should break down the Prompt before actually looking at the Statements carefully, but it's all on one big screen in front of you, and that's okay -- use everything you can see to determine the correct approach. _________________ Prep Smarter, Score Higher www.knewton.com Dive right in with Knewton. Summer savings on GMAT Prep for$349 + additional $900 Mega Bonus from BTG. Enroll TODAY. Senior | Next Rank: 100 Posts Joined 30 Mar 2010 Posted: 45 messages go on with A Since x=y-a x+a=y squaring on both sides we get (x+a)^2=y^2 go on with B x=y+a x-a=y squaring on both sides we get not possible to get (x+a)^2=y^2 opt A is correct Senior | Next Rank: 100 Posts Joined 27 Mar 2011 Posted: 40 messages Upvotes: 2 Only option A can help determine if the eqation holds true or not as value of variable a can be "Zero". Master | Next Rank: 500 Posts Joined 25 Aug 2011 Posted: 101 messages the answer should be A.just substitute the value of x=y-a form first statetment in the question that is (y-a+a)^2which is equal to y^2 hence proved. • Magoosh Study with Magoosh GMAT prep Available with Beat the GMAT members only code • Get 300+ Practice Questions 25 Video lessons and 6 Webinars for FREE Available with Beat the GMAT members only code • FREE GMAT Exam Know how you'd score today for$0

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