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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 If a and b are constants, is the expression tagged by: AbeNeedsAnswers This topic has 2 expert replies and 0 member replies Timer 00:00 Your Answer A B C D E Global Stats Difficult If a and b are constants, is the expression (x+b)/(√(x+a)) defined for x = -2 ? (1) a = 5 (2) b = 6 A Source: Official Guide 2020 GMAT/MBA Expert GMAT Instructor Joined 08 Dec 2008 Posted: 13001 messages Followed by: 1250 members Upvotes: 5254 GMAT Score: 770 AbeNeedsAnswers wrote: If a and b are constants, is the expression (x+b)/(√(x+a)) defined for x = -2 ? (1) a = 5 (2) b = 6 Target question: Is the expression defined for x = -2? This is a great candidate for rephrasing the target question. If x = -2, then the expression becomes (-2)+b/√(-2+a) There are two ways in which the expression(-2)+b/√(-2+a) is NOT defined: case i) If a = 2, then the fraction's denominator is 0, which means the entire rational expression is NOT defined. case ii) If a < 2, then the value inside the square root sign is NEGATIVE, in which case the denominator is NOT defined. When we combine both cases, we see that the expression is NOT defined when a ≤ -2 Or we can say, the expression IS defined when a > -2 REPHRASED target question: Is a > -2? Aside: Here’s a video with tips on rephrasing the target question: http://www.gmatprepnow.com/module/gmat-data-sufficiency?id=1100 Statement 1: a = 5 The answer to the REPHRASED target question is YES, a IS greater than -2 Since we can answer the REPHRASED target question with certainty, statement 1 is SUFFICIENT Statement 2: b = 6 This does not help us answer the REPHRASED target question. Statement 2 is NOT SUFFICIENT Answer: A Cheers, Brent _________________ Brent Hanneson – Creator of GMATPrepNow.com Use my video course along with Sign up for free Question of the Day emails And check out all of these free resources GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMAT’s FREE 60-Day Study Guide and reach your target score in 2 months! GMAT/MBA Expert Elite Legendary Member Joined 23 Jun 2013 Posted: 10197 messages Followed by: 496 members Upvotes: 2867 GMAT Score: 800 Hi All, We're told that A and B are constants. We're asked if the expression (X+B)/(√(X+A)) is "defined" for x = -2. This is a YES/NO question and is a great 'concept' question - meaning that you don't have to do much math if you understand the concepts involved. For the given fraction to be 'defined', the denominator CANNOT be 0. As such, since we're given a value for X (re: -2), we need to know the value for A to answer this question. 1) A = 5 Fact 1 gives us the value of A. With the given value of X, we know that the denominator will be a POSITIVE number, so the fraction will be defined and the answer to the question is ALWAYS YES. Fact 1 is SUFFICIENT 2) B = 6 Fact 2 gives us information to define the numerator of the fraction (re: -2 + 6 = +4), but not the denominator. IF.... A = +2, then the answer to the question is NO A = +3, then the answer to the question is YES Fact 2 is INSUFFICIENT Final Answer: A GMAT assassins aren't born, they're made, Rich • Free Veritas GMAT Class Experience Lesson 1 Live Free Available with Beat the GMAT members only code • 1 Hour Free BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • 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 Practice Test & Review How would you score if you took the GMAT Available with Beat the GMAT members only code • 5-Day Free Trial 5-day free, full-access trial TTP Quant Available with Beat the GMAT members only code • 5 Day FREE Trial Study Smarter, Not Harder Available with Beat the GMAT members only code • FREE GMAT Exam Know how you'd score today for$0

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