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Given:

[tex]\[
\frac{9^n \cdot 3^2 \cdot 3^n - (27)^n}{\left(3^m \cdot 2\right)^{3^3}} = 3^{-3}
\][/tex]

Show that:

[tex]\[
m - n = 1
\][/tex]


Sagot :

To solve the given equation

[tex]\[ \frac{9^n \cdot 3^2 \cdot 3^n - 27^n}{(3^m \cdot 2)^{27}} = 3^{-3} \][/tex]

let's start by simplifying both the numerator and the denominator.

First, simplify the expressions in the numerator:

1. [tex]\(9^n\)[/tex] can be written as [tex]\((3^2)^n = 3^{2n}\)[/tex].
2. [tex]\(3^2\)[/tex] is [tex]\(9\)[/tex] or [tex]\(3^2\)[/tex].
3. [tex]\(3^n\)[/tex] is itself [tex]\(3^n\)[/tex].
4. [tex]\(27^n\)[/tex] can be written as [tex]\((3^3)^n = 3^{3n}\)[/tex].

Using these equivalences, the numerator becomes:

[tex]\[ 9^n \cdot 3^2 \cdot 3^n - 27^n = 3^{2n} \cdot 3^2 \cdot 3^n - 3^{3n} \][/tex]

Next, combine the exponents of 3 in the simplified numerator:

[tex]\[ 3^{2n} \cdot 3^2 \cdot 3^n = 3^{(2n + 2 + n)} = 3^{(3n + 2)} \][/tex]

Thus, the numerator simplifies to:

[tex]\[ 3^{3n + 2} - 3^{3n} \][/tex]

Now, simplify the denominator:

[tex]\[ (3^m \cdot 2)^{27} \][/tex]

Raise each term to the power of 27:

[tex]\[ 3^{27m} \cdot 2^{27} \][/tex]

Now the equation can be rewritten as:

[tex]\[ \frac{3^{3n + 2} - 3^{3n}}{3^{27m} \cdot 2^{27}} = 3^{-3} \][/tex]

For the right-hand side to equal [tex]\(3^{-3}\)[/tex], the terms involving powers of 3 in the numerator and denominator must be consistent in their exponents.

To equate the exponents of 3, let's express the powers clearly.

From the left-hand side, focus on the most significant terms involving powers of 3. Collect the exponent terms:

[tex]\[ 3^{3n + 2} - 3^{3n} \][/tex]

If we factor out [tex]\(3^{3n}\)[/tex] from the numerator:

[tex]\[ 3^{3n}(3^2 - 1) = 3^{3n} \cdot 8 = 3^{3n} \cdot 2^3 \][/tex]

Thus, the equation becomes:

[tex]\[ \frac{3^{3n} \cdot 2^3}{3^{27m} \cdot 2^{27}} = 3^{-3} \][/tex]

Now, simplifying the fractions:

[tex]\[ \frac{3^{3n} \cdot 2^3}{3^{27m} \cdot 2^{27}} = \frac{3^{3n}}{3^{27m}} \cdot \frac{2^3}{2^{27}} = 3^{3n-27m} \cdot 2^{3-27} \][/tex]

We know this equals [tex]\(3^{-3}\)[/tex]. So that gives us two separate equations for the exponents. The exponent of 3:

[tex]\[ 3n - 27m = -3 \][/tex]

The exponent of 2:

[tex]\[ 3 - 27 = -24 \][/tex]

These two should hold true. For the exponent of 3:

[tex]\[ 3n - 27m = -3 \implies n - 9m = -1 \implies m - n = 1 \][/tex]

Therefore, we have shown that:

[tex]\[ m - n = 1 \][/tex]
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