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Each week we'll be posting several questions from The Official Guide for GMAT® Review, 13th Edition and then after couple of days we'll provide Official Answer (OA) to them along with a slution.

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Re: If x is an integer, is 9^x + 9^{-x} = b ? [#permalink]
01 Oct 2012, 04:20

2

This post received KUDOS

Expert's post

SOLUTION

If x is an integer, is 9^x + 9^{-x} = b ?

(1) 3^x + 3^{-x} = \sqrt{b + 2} --> square both sides --> 9^x+2*3^x*\frac{1}{3^x}+9^{-x}=b+2 --> 9^x + 9^{-x} = b. So answer to the question is YES. Sufficient.

Re: If x is an integer, is 9^x + 9^{-x} = b ? [#permalink]
04 Oct 2012, 13:44

1

This post received KUDOS

Expert's post

SOLUTION

If x is an integer, is 9^x + 9^{-x} = b ?

(1) 3^x + 3^{-x} = \sqrt{b + 2} --> square both sides --> 9^x+2*3^x*\frac{1}{3^x}+9^{-x}=b+2 --> 9^x + 9^{-x} = b. So answer to the question is YES. Sufficient.

(2) x > 0. No sufficient.

Answer: A.

Kudos points given to everyone with correct solution. Let me know if I missed someone. _________________

Re: If x is an integer, is 9^x + 9^{-x} = b ? [#permalink]
31 Oct 2012, 22:40

Bunuel wrote:

SOLUTION

If x is an integer, is 9^x + 9^{-x} = b ?

(1) 3^x + 3^{-x} = \sqrt{b + 2} --> square both sides --> 9^x+2*3^x*\frac{1}{3^x}+9^{-x}=b+2 --> 9^x + 9^{-x} = b. So answer to the question is YES. Sufficient.

(2) x > 0. No sufficient.

Answer: A.

Kudos points given to everyone with correct solution. Let me know if I missed someone.

Question please: Can we do anything with the 9^x + 9^{-x} = b or simplify any more than what is given? I tried to do something more but could not find anything proper...

Re: If x is an integer, is 9^x + 9^{-x} = b ? [#permalink]
01 Nov 2012, 06:25

Expert's post

ikokurin wrote:

Bunuel wrote:

SOLUTION

If x is an integer, is 9^x + 9^{-x} = b ?

(1) 3^x + 3^{-x} = \sqrt{b + 2} --> square both sides --> 9^x+2*3^x*\frac{1}{3^x}+9^{-x}=b+2 --> 9^x + 9^{-x} = b. So answer to the question is YES. Sufficient.

(2) x > 0. No sufficient.

Answer: A.

Kudos points given to everyone with correct solution. Let me know if I missed someone.

Question please: Can we do anything with the 9^x + 9^{-x} = b or simplify any more than what is given? I tried to do something more but could not find anything proper...

I'd say 9^x + 9^{-x} the simplest way of writing this expression and as you can see from the solution we don't even need to manipulate with it further to answer the question. _________________

Re: If x is an integer, is 9^x + 9^{-x} = b ? [#permalink]
07 Jan 2014, 07:43

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