Log Puzzle: (log₂x · log₃x)/(log₂x + log₃x) = 2
October 31, 2024 2025-10-31 15:22Log Puzzle: (log₂x · log₃x)/(log₂x + log₃x) = 2
What value of \(x\) satisfies \(\displaystyle \frac{\log_2 x \cdot \log_3 x}{\log_2 x + \log_3 x} = 2\)?
Log equation. Convert to reciprocals, change base to \(x\), and squeeze everything into a single log: \(\log_x 6 = \tfrac12 \Rightarrow x=36\).
🧭 Problem
What value of \(x\) satisfies \[ \frac{\log_2 x \cdot \log_3 x}{\log_2 x + \log_3 x} = 2 ? \]
1️⃣ Clear the fraction
Start with the given:
Multiply both sides by \((\log_2 x + \log_3 x)\):
2️⃣ Turn it into a “sum of reciprocals”
Divide both sides by \(\log_2 x \cdot \log_3 x\):
Now use the change-of-base identity \(\displaystyle \frac{1}{\log_a b} = \log_b a\):
So we get
3️⃣ Combine the logs
Since \(\log_x 3 + \log_x 2 = \log_x (3\cdot 2) = \log_x 6\), we have:
Convert the log back to exponential form:
Check the options: \(\boxed{36}\) is option (C).
📝 Quick Check
What value of \(y\) satisfies \[ \frac{\log_2 y \cdot \log_5 y}{\log_2 y + \log_5 y} = 2 ? \]