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101學測數學考科-05


<單選>若正實數 \(x, y\) 滿足 \(\log_{10} x = 2.8\),\(\log_{10} y = 5.6\),則 \(\log_{10} (x^2 + y)\) 最接近下列哪一個選項的值?
(1) 2.8
(2) 5.6
(3) 5.9
(4) 8.4
(5) 11.2

答案

根據題意,\(x = 10^{2.8}\),\(y = 10^{5.6}\)。因此,\(x^2 = 10^{5.6}\),所以 \(x^2 + y = 10^{5.6} + 10^{5.6} = 2 \times 10^{5.6}\)。因此,\(\log_{10} (x^2 + y) = \log_{10} (2 \times 10^{5.6}) = \log_{10} 2 + 5.6 \approx 0.3010 + 5.6 = 5.901\)。因此,正確答案是 (3) 5.9。 報錯
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