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guddo
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This problem is probably related just to calculation ( which will eat up time unless we find a shortcut ) :

3^(x - 3) * (3^3 - 1) = 2106
3^(x - 3) * 26 = 2106
3^(x - 3) * 13 = 1053

We may notice the fact that IFF we multiply 13 with powers of 3 : 3^0 , 3^4 , 3^8 ... it gives 3 in the unit's place
Hence 13 * ( something that is a odd power of 3) 81 fits this nicely since 81*10 810 , hence 81*13 is bound to be 1053 :lol:
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guddo

Asked: If \(3^x - 3^{x - 3} = 2,106\), what is the value of x?

\(3^{x-3} (3^3 - 1) = 2106 = 2*13*3^4\)
x - 3 = 4
x =7

\(3^7 - 3^4 = 3^4 (3^3 - 1) = 3^4 *26= 2*13*3^4\)

IMO D
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­Hi Bunuel - I understand most of the steps but am unclear of the result when factoring. If the original equation is 3^x - 3^x-3 and you are looking to factor out the second segment (3^x-3) .. what happens to the first part? How do we end up with 3^3 - 1 ? ..... thank you
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edthehead7
­Hi Bunuel - I understand most of the steps but am unclear of the result when factoring. If the original equation is 3^x - 3^x-3 and you are looking to factor out the second segment (3^x-3) .. what happens to the first part? How do we end up with 3^3 - 1 ? ..... thank you
\(­3^x = 3^{x-3}*3^3\). So, wwhen you factor out \(3^{x-3}\) you are left with only \(3^3\).­
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guddo
If \(3^x - 3^{x - 3} = 2,106\), what is the value of x?

A. 10
B. 9
C. 8
D. 7
E. 6

Attachment:
2024-01-26_13-12-27.png
\(3^x\) is way bigger than \(3^{x-3}\)

Therefore, \(3^x\) is approximately equal to, but slightly greater than 2,106.

\(3^6\) = 729 and \(3^7\) = 2,187

x = 7

Answer: D.
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