To identify the original base of the expression \( \frac{\log_2 128}{\log_2 32} \) before the change of base formula was applied, we can apply the property of logarithms that relates the change of base formula to the original expression.
The change of base formula is:
\[ \log_a b = \frac{\log_c b}{\log_c a} \]
This means we can find a common logarithm (base \( c \)) for both \( 128 \) and \( 32 \). Specifically, using the base \( 2 \), we have:
\[ \frac{\log_2 128}{\log_2 32} = \log_{32} 128 \]
Thus, the original expression before applying the change of base was:
\[ \log_{32} 128 \]
So, the base of the original expression was \( 32 \).