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Using the change-of-base formula, which of the following is equivalent to the logarithmic expression below?

[tex]\[ \log_7 18 \][/tex]

A. [tex]\(\frac{\log_{18} 10}{\log_7 10}\)[/tex]

B. [tex]\(\frac{\log_{11} 18}{\log_{10} 11}\)[/tex]

C. [tex]\(\frac{\log_{10} 7}{\log_{10} 18}\)[/tex]

D. [tex]\(\frac{\log_{10} 18}{\log_{10} 7}\)[/tex]

Sagot :

To determine which of the given options is equivalent to the logarithmic expression [tex]\(\log_7 18\)[/tex], we can use the change-of-base formula for logarithms. The change-of-base formula states:

[tex]\[ \log_b(a) = \frac{\log_c(a)}{\log_c(b)} \][/tex]

In this formula, [tex]\(a\)[/tex] is the argument of the logarithm, [tex]\(b\)[/tex] is the base of the logarithm, and [tex]\(c\)[/tex] is any new base that we choose to use for the logarithms in the numerator and denominator.

For the given expression [tex]\(\log_7 18\)[/tex], we want to find an equivalent expression using base 10 logarithms (common logarithms), as it is commonly used. Applying the change-of-base formula to [tex]\(\log_7 18\)[/tex], we get:

[tex]\[ \log_7 18 = \frac{\log_{10}(18)}{\log_{10}(7)} \][/tex]

Next, let's match this result with the given choices to identify the correct equivalent expression.

The provided options are:

A. [tex]\(\frac{\log_{18} 10}{\log_7 10}\)[/tex]
B. [tex]\(\frac{\log_{11} 18}{\log_{10} 11}\)[/tex]
C. [tex]\(\frac{\log_{10} 7}{\log_{10} 18}\)[/tex]
D. [tex]\(\frac{\log_{10} 18}{\log_{10} 7}\)[/tex]

By comparing our derived expression [tex]\(\frac{\log_{10}(18)}{\log_{10}(7)}\)[/tex] with the options, we can see that option D matches perfectly:

[tex]\[ \frac{\log_{10} 18}{\log_{10} 7} \][/tex]

Therefore, the correct answer is:

[tex]\[ \boxed{4} \][/tex]