To establish that \( \log(10^7 \cdot 5) = 7 + \log 5 \), the correct first step involves using the property of logarithms related to multiplication. Specifically, the product rule states that \( \log(a \cdot b) = \log a + \log b \).
Thus, the correct response is:
The first step is to rewrite the expression using addition, such that \( \log(10^7 \cdot 5) = \log 10^7 + \log 5 \).