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Re: If 3^(2n) = (1/9)^(n+2), what is the value of n? [#permalink]
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Carcass wrote:
If \(3^{(2n)} = (\frac{1}{9})^{(n+2)}\), what is the value of n?

A. -2
B. -1
C. 0
D. 1
E. 2


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Question part of the project GRE Quantitative Reasoning Daily Challenge - (2021) EDITION
GRE - Math Book


For these kinds of questions, we typically must rewrite the terms so that they have the SAME BASES.
One option is to rewrite the right hand side with a power of 3.

Given: 3^(2n) = (1/9)^(n + 2)
Rewrite 1/9 to get: 3^(2n) = [3^(-2)]^(n + 2)
Apply Power of a Power law to get: 3^(2n) = 3^(-2n - 4)
We can now conclude that 2n = -2n - 4
Solve, to get: n = -1
Answer: B

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If 3^(2n) = (1/9)^(n+2), what is the value of n? [#permalink]
Carcass wrote:
If \(3^{(2n)} = (\frac{1}{9})^{(n+2)}\), what is the value of n?

A. -2
B. -1
C. 0
D. 1
E. 2



\(3^{2n} = (\frac{1}{9})^{(n+2)}\)

\(9^n = (9^{-1})^{(n+2)}\)

\(9^n = 9^{(-n-2)}\)

Property: When the bases are equal, then the powers are also equal.

\(n = -n-2\)
\(2n = -2\)
\(n = -1\)

Hence, option B
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