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Exponents question from OG 11

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by Osirus@VeritasPrep » Tue Jan 26, 2010 5:46 am
If x is an integer, is 9^(x) + 9 ^(-x) = b?

(1) 3^(x) + 3^(-x) = sqrt(b +2)

(2) x> 0 = b

OA A







My question is if x is greater than 0 and b = 0 what possible positive number can x equal for the statement in the stem to equal zero? How is statement (2) insufficient?
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Source: — Data Sufficiency |
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by thephoenix » Tue Jan 26, 2010 6:41 am
clearly with S2) we are no where

s1)3^x+3^-x=sqrt(b+2)
square bth side

(3^x+3^-x)^2=b+2
3^2x+3^-2x+2=b+2
9^x+9^-x=b
hence suff

hence A
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by Osirus@VeritasPrep » Tue Jan 26, 2010 6:43 am
thephoenix wrote:clearly with S2) we are no where

s1)3^x+3^-x=sqrt(b+2)
square bth side

(3^x+3^-x)^2=b+2
3^2x+3^-2x+2=b+2
9^x+9^-x=b
hence suff

hence A
That's what the official guide says. I understand that it doesn't allow you to manipulate the problem in anyway, but conceptually how can b = 0 and x be positive and the condition in the prompt not be true? What possible number could x be to make that statement false?
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by thephoenix » Tue Jan 26, 2010 7:15 am
osirus0830 wrote:If x is an integer, is 9^(x) + 9 ^(-x) = b?

(1) 3^(x) + 3^(-x) = sqrt(b +2)

(2) x> 0 = b

OA A

My question is if x is greater than 0 and b = 0 what possible positive number can x equal for the statement in the stem to equal zero? How is statement (2) insufficient?
in the prev one i missed your query

you have given s2) wrong act in OG 11 its q no 142
s2) IS JUST X>0

WITH YOUR VERSION OF S2) I GUESS THE ANS SUD BE D
but then all mathematician wud have gone crazy to solve that bcoz either the exp
9^2x=-1 is false or this world is false(i hope which is not)

so let us stick to original i.e with only x>2 its insuff to prove anything
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by Osirus@VeritasPrep » Tue Jan 26, 2010 7:20 am
thephoenix wrote:
osirus0830 wrote:If x is an integer, is 9^(x) + 9 ^(-x) = b?

(1) 3^(x) + 3^(-x) = sqrt(b +2)

(2) x> 0 = b

OA A

My question is if x is greater than 0 and b = 0 what possible positive number can x equal for the statement in the stem to equal zero? How is statement (2) insufficient?
in the prev one i missed your query

you have given s2) wrong act in OG 11 its q no 142
s2) IS JUST X>0

WITH YOUR VERSION OF S2) I GUESS THE ANS SUD BE D
but then all mathematician wud have gone crazy to solve that bcoz either the exp
9^2x=-1 is false or this world is false(i hope which is not)

so let us stick to original i.e with only x>2 its insuff to prove anything
Ah, thanks
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