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108學測數學考科-05


<單選題>設正實數\(b\)滿足 \(\log(100)(\log b) + \log 100 + \log b = 7\),試選出正確的選項。
(1) \(1 \leq b \leq \sqrt{10}\)
(2) \(\sqrt{10} \leq b \leq 10\)
(3) \(10 \leq b \leq 10\sqrt{10}\)
(4) \(10\sqrt{10} \leq b \leq 100\)
(5) \(100 \leq b \leq 100\sqrt{10}\)。

答案

\(\log 100 = 2\),原式化為\(2\log b + 2 + \log b = 7 \Rightarrow 3\log b = 5 \Rightarrow \log b = \frac{5}{3}\),故\(b=10^{5/3}\)。因\(10^{3/2} = 10\sqrt{10} \lt 10^{5/3} \lt 10^2 = 100\),故選(4)。答案:(4) 報錯
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