To establish that \( \log(10^7 \cdot 5) = 7 + \log 5 \), the first step is to rewrite the expression using the property of logarithms that states \( \log(ab) = \log a + \log b \). This leads us to the equation:
\[ \log(10^7 \cdot 5) = \log(10^7) + \log(5) \]
Here, since \( \log(10^7) = 7 \) (by the definition of logarithms), we can then express it as:
\[ \log(10^7) + \log(5) = 7 + \log(5) \]
Thus, the correct response is:
The first step is to rewrite the expression using addition, such that \( \log(10^7 \cdot 5) = \log(10^7) + \log(5) \).