Which of the following is equivalent to [tex]4 \ln (3 x)[/tex] for [tex]x \ \textgreater \ 0[/tex]?

[tex]
\begin{array}{l}
\ln 81 + \ln x \\
\ln (12 x) \\
\ln 12 + \ln x \\
\ln \left(81 x^4\right)
\end{array}
[/tex]

Choose the correct answer below.

A. [tex]\ln 81 + \ln x[/tex]
B. [tex]\ln (12 x)[/tex]
C. [tex]\ln 12 + \ln x[/tex]
D. [tex]\ln \left(81 x^4\right)[/tex]



Answer :

To determine which of the following expressions is equivalent to [tex]\(4 \ln (3 x)\)[/tex] for [tex]\(x > 0\)[/tex], let's break down the given expression using logarithmic properties step-by-step.

1. Given Expression:
[tex]\(4 \ln (3 x)\)[/tex]

2. Using the Power Rule of Logarithms:
The power rule [tex]\(a \ln b = \ln (b^a)\)[/tex] can be applied to simplify the expression:
[tex]\[ 4 \ln (3 x) = \ln \left((3 x)^4\right) \][/tex]

3. Expand the Argument:
Next, expand [tex]\((3 x)^4\)[/tex]:
[tex]\[ (3 x)^4 = 3^4 \cdot x^4 = 81 \cdot x^4 \][/tex]

4. Simplify the Logarithm:
Substitute back into the logarithm:
[tex]\[ \ln \left((3 x)^4\right) = \ln (81 x^4) \][/tex]

Now we have:
[tex]\[ 4 \ln (3 x) = \ln (81 x^4) \][/tex]

We see that the expression [tex]\(\ln (81 x^4)\)[/tex] exactly matches one of the provided options. Therefore, the correct answer is:
[tex]\[ \boxed{\ln \left(81 x^4\right)} \][/tex]

5. Verification against Options:
- [tex]\(\ln 81 + \ln x\)[/tex]
- [tex]\(\ln (12 x)\)[/tex]
- [tex]\(\ln 12 + \ln x\)[/tex]
- [tex]\(\ln \left(81 x^4\right)\)[/tex]

The expression equivalent to [tex]\(4 \ln (3 x)\)[/tex] matches [tex]\(\ln \left(81 x^4\right)\)[/tex].

Thus, the correct answer is:
[tex]\[ 4 \ln (3 x) \equiv \ln \left(81 x^4\right) \][/tex]

Choose the correct answer below:
[tex]\( \ln \left(81 x^4\right) \)[/tex]

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