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If x ¤ y = (x + y)² - (x - y)² Then √5 ¤ √5 =
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Updated on: 13 May 2016, 06:47
X = √5 and Y also =√5 Applying the function (√5+√5)^2 - (√5-√5)^2 = (2√5)^2 - 0 = 4 x 5 = 20. Answer is E.
Note: Alternative Approach is the entire function is represented as X^2 - Y^2 = (X+Y)(X-Y) which can be simplified as (x+y+x-y)(x+y-(x-y)) = (2x)(2y)=4xy. Substituting x=√5 and y = √5 you get the answer 20.
Originally posted by Senthil7 on 13 May 2016, 06:43.
Last edited by Senthil7 on 13 May 2016, 06:47, edited 1 time in total.
Re: If x ¤ y = (x + y)² - (x - y)² Then √5 ¤ √5 =
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26 Aug 2016, 11:39
Top Contributor
Bunuel wrote:
If x ¤ y = (x + y)² - (x - y)². Then √5 ¤ √5 =
A. 0 B. 5 C. 10 D. 15 E. 20
This is a great questions that typifies what I love about most GMAT math questions: they can almost always be solved in more than 1 way.
One option is to plug the values into the "recipe" and get... √5 ¤ √5 = (√5 + √5)² - (√5 - √5)² = (2√5)² - (0)² = (2√5)(2√5) = 4√25 = 20 = D
Another option is to simplify the recipe before plugging in the values x ¤ y = (x + y)² - (x - y)² = (x² + 2xy + y²) - (x² - 2xy + y²) = 4xy So, x ¤ y = 4xy NOW plug in the values to get.... √5 ¤ √5 = 4(√5)(√5) = 4√25 = 20 = D
Re: If x ¤ y = (x + y)² - (x - y)² Then √5 ¤ √5 =
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04 Mar 2019, 07:59
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