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问题: 求证

求证对数的换底公式.

解答:

换底公式:log(a)N = log(c)N / log(c)a

证明:设 log(a)N = x
则 N = a^x
两边同取以c为底的对数得 log(c)N = log(c)(a^x) = x*log(c)a
所以 x = log(c)N / log(c)a
故 log(a)N = log(c)N / log(c)a


特别地 log(a)b = log(b)b / log(b)a = 1 / log(b)a