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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 ## Algebra tagged by: BTGmoderatorRO ##### This topic has 2 expert replies and 0 member replies ## Algebra $$If\ x+y=a\ and\ x-y=b,\ then\ 2xy=?$$ $$\left(a\right)\ \frac{\left(a^2-b^2\right)}{2}$$ $$\left(b\right)\ \frac{\left(b^2-a^2\right)}{2}$$ $$\left(c\right)\ \frac{\left(a^{ }-b\right)}{2}$$ $$\left(d\right)\ \frac{\left(ab\right)}{2}$$ $$\left(e\right)\ \frac{\left(a^2+b^2\right)}{2}$$ OA is a How do i set up the formula here to get the right answer to this question? Thank you for your help ### GMAT/MBA Expert Elite Legendary Member Joined 23 Jun 2013 Posted: 10197 messages Followed by: 497 members Upvotes: 2867 GMAT Score: 800 Hi Roland2rule, This question can be approached in a couple of different ways, Here's how you can TEST VALUES to get to the answer: IF... X=3 and Y=2 A=5 and B=1 So we're looking for an answer that equals (2)(3)(2) = 12 when A=5 and B=1. There's only one answer that matches... Final Answer: A GMAT assassins aren't born, they're made, Rich _________________ Contact Rich at Rich.C@empowergmat.com ### GMAT/MBA Expert GMAT Instructor Joined 04 Oct 2017 Posted: 551 messages Followed by: 11 members Upvotes: 180 Quote: $$If\ x+y=a\ and\ x-y=b,\ then\ 2xy=?$$ $$\left(a\right)\ \frac{\left(a^2-b^2\right)}{2}$$ $$\left(b\right)\ \frac{\left(b^2-a^2\right)}{2}$$ $$\left(c\right)\ \frac{\left(a^{ }-b\right)}{2}$$ $$\left(d\right)\ \frac{\left(ab\right)}{2}$$ $$\left(e\right)\ \frac{\left(a^2+b^2\right)}{2}$$ OA is a How do i set up the formula here to get the right answer to this question? Thank you for your help Hi Roland2rule, Lets take a look at your question, We can use this problem using the formula: $$\left(x+y\right)^2-\left(x-y\right)^2=4xy$$ Plugin the given values, $$a^2-b^2=4xy$$ $$a^2-b^2=2\times2xy$$ $$\frac{a^2-b^2}{2}=2xy$$ $$2xy=\frac{a^2-b^2}{2}$$ Therefore, option A is correct. Hope it helps. I am available if you'd like any follow up. _________________ GMAT Prep From The Economist We offer 70+ point score improvement money back guarantee. Our average student improves 98 points. Free 7-Day Test Prep with Economist GMAT Tutor - Receive free access to the top-rated GMAT prep course including a 1-on-1 strategy session, 2 full-length tests, and 5 ask-a-tutor messages. Get started now. • Magoosh Study with Magoosh GMAT prep Available with Beat the GMAT members only code • 1 Hour Free BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • Free Veritas GMAT Class Experience Lesson 1 Live Free Available with Beat the GMAT members only code • 5 Day FREE Trial Study Smarter, Not Harder 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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