駭客數學p7-23

[gncpkat]

(B)求滿足 (log底數2真數x) * (log底數2真數x+1) <=2 之整數解的個數？
(A)1個 (B)2個 (C)3個 (D)4個

[thepiano]

令 S = log(x，2) * log(x+1，2)
x = 1，S = 0
x = 2，S = log(3，2) < 2
x ≧ 3，S ≧ log(3，2) * 2 > log(2，2) * 2 = 2
故僅有二解

[gncpkat]

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