To find \( \log_4(16 \cdot 64) \) using the property \( \log_b(xy) = \log_b(x) + \log_b(y) \), we first rewrite the expression:
\[ \log_4(16 \cdot 64) = \log_4(16) + \log_4(64) \]
Next, we need to calculate \( \log_4(16) \) and \( \log_4(64) \).
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Calculate \( \log_4(16) \): \[ 16 = 4^2 \implies \log_4(16) = 2 \]
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Calculate \( \log_4(64) \): \[ 64 = 4^3 \implies \log_4(64) = 3 \]
Now, we can add these results together:
\[ \log_4(16 \cdot 64) = \log_4(16) + \log_4(64) = 2 + 3 = 5 \]
Thus, the final answer is:
\[ \log_4(16 \cdot 64) = 5 \]