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Re: What is the value of x^2 + y^2 ? [#permalink]
01 Dec 2014, 03:11

1

This post received KUDOS

What is the value of x^2 + y^2 ?

(1) x^2 + y^2 = 2xy + 1 (2) x^2 + y^2 = 4 - 2xy

---------------------------------------------------------------------------------------------------------------------------------------- Good tricky question almost carried away and started finding (x+y) ^2

but finally marked correct ans C

1. x^2 + y^2 = 2xy+1 --> value of 2XY is not known hence not sufficient 2. x^2 + y^2 = 4-2xy --> value of 2XY is not known hence not sufficient

Re: What is the value of x^2 + y^2 ? [#permalink]
26 Aug 2012, 09:41

Expert's post

When trying to solve for x and y, it doesn't appear that we can find a solution for x^2 + y^2 2xy + 1 = 4 - 2xy

4xy = 3 xy = 3/4

However, the approach of canceling out 2xy DOES remove the xy variable and leaves us cleanly with x^2 + y^2. We indeed have the value as you mentioned...perhaps the source for the OA is incorrect. _________________

well metallicafan, i see nothing wrong with your approach, but i solved this the following way... (1) x^2 + y^2 = 2.x.y + 1 => (x - y)^2 = 1 => x - y = 1 or -1 insuff

(2) x^2 + y^2 = 4 - 2.x.y => (x + y)^2 = 4 => x + y = 2 or -2 insuff

combining the two, since the above equations can have multiple values when we solve for x and y, hence, insufficient. answer is E. is this a GMATPrep question?? because i dont think the real gmat would confuse students like this.

well metallicafan, i see nothing wrong with your approach, but i solved this the following way... (1) x^2 + y^2 = 2.x.y + 1 => (x - y)^2 = 1 => x - y = 1 or -1 insuff

(2) x^2 + y^2 = 4 - 2.x.y => (x + y)^2 = 4 => x + y = 2 or -2 insuff

combining the two, since the above equations can have multiple values when we solve for x and y, hence, insufficient. answer is E. is this a GMATPrep question?? because i dont think the real gmat would confuse students like this.

happy to help, a kudos if you like.

But don't you get an answer of 5/2 for\(x^2 + y^2\) if you take any of the combinations?, Note that we are asked to find \(x^2 + y^2\)

well metallicafan, i see nothing wrong with your approach, but i solved this the following way... (1) x^2 + y^2 = 2.x.y + 1 => (x - y)^2 = 1 => x - y = 1 or -1 insuff

(2) x^2 + y^2 = 4 - 2.x.y => (x + y)^2 = 4 => x + y = 2 or -2 insuff

combining the two, since the above equations can have multiple values when we solve for x and y, hence, insufficient. answer is E. is this a GMATPrep question?? because i dont think the real gmat would confuse students like this.

happy to help, a kudos if you like.

But don't you get an answer of 5/2 for\(x^2 + y^2\) if you take any of the combinations?, Note that we are asked to find \(x^2 + y^2\)

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