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Re: Which value(s) of x satisfies the equation above? [#permalink]

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02 Nov 2014, 22:09

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Since only X = 9 is given and it satisfies the condition Answer is B

Hey Ashishmathew, (2x-2)^2 = 4x^2 +4-8x right ? How come ur LHS of the eqn is \(4x^2 - 4x + 3\) ? Or Am I missing out something here ?

Dear sreelakshmigs I'm happy to respond.

First of all, Ashishmathew01081987's solution is not correct at all. You are perfectly correct: \((2x-2)^2 = 4x^2 - 8x + 4\) Also, the factoring thing he does at the end, the steps after x(x - 4) = 9, are 100% incorrect. If you want to see the correct solution to this problem, see: http://magoosh.com/gmat/2013/gmat-math- ... -radicals/

Mike
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Re: Which value(s) of x satisfies the equation above? [#permalink]

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03 Nov 2014, 21:48

Hey Ashishmathew, (2x-2)^2 = 4x^2 +4-8x right ? How come ur LHS of the eqn is \(4x^2 - 4x + 3\) ? Or Am I missing out something here ?[/quote] Dear sreelakshmigs I'm happy to respond.

First of all, Ashishmathew01081987's solution is not correct at all. You are perfectly correct: \((2x-2)^2 = 4x^2 - 8x + 4\) Also, the factoring thing he does at the end, the steps after x(x - 4) = 9, are 100% incorrect. If you want to see the correct solution to this problem, see: http://magoosh.com/gmat/2013/gmat-math- ... -radicals/

Mike [/quote]

Thanks Sree for pointing out my mistake. That was a blunder. Hope that it doesn't happen on the GMAT.

Thanks Mike, I understand why the factoring stuff would have led me into the trap. Plugging numbers is the best option here.

Thanks Sree for pointing out my mistake. That was a blunder. Hope that it doesn't happen on the GMAT.

Thanks Mike, I understand why the factoring stuff would have led me into the trap. Plugging numbers is the best option here.

Dear Ashishmathew01081987, Actually, it's very good to understand the algebra in this problem. Again, you can see a full algebraic solution at the blog to which I linked. Plugging numbers is good sometimes, but it's best not to make that a one-size-fit-all kind of strategy. Does this make sense? Mike
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Education is not the filling of a pail, but the lighting of a fire. — William Butler Yeats (1865 – 1939)

Re: Which value(s) of x satisfies the equation above? [#permalink]

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23 Jun 2016, 19:39

Hello from the GMAT Club BumpBot!

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Which value(s) of x satisfies the equation above? [#permalink]

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12 Nov 2017, 10:24

Zarrolou wrote:

Using numbers:

\(2x - 2 = \sqrt{3x^2+13}\)

I)-1

\(-4= \sqrt{3(-1)^2+13}\)

\(\sqrt{3+13}\) does not equal \(-4\) , so \(-1\) is NOT a possible value.

If we take a look at the possible answer, all contain I except B. So B is the correct answer

I think this might be incorrect.

First, -4 = 16^(1/2) is as correct answer since (-4)(-4) = 16. Second, the bold part is not correct. x² when x = -1 is the same as -1² = -1 and not (-1)² = 1, so we should have -4 = 10^(1/2). So, option I is incorrect. Since the only option that says I is incorrect is B, then, B is our answer.