F.4maths對數函數

2014-05-25 10:37 pm
求下列各式的值。

1. 5㏒27 2 - ㏒27 18 - 2㏒27 4

註:27是在㏒的下面(下標),27的字數較小。

謝謝!!

回答 (1)

2014-05-25 10:51 pm
✔ 最佳答案
1.

5 log27 2 - log27 18 - 2 log274

= log27 2⁵ - log27 18 - log274²

= log27 32 - log27 18 - log27 16

= log27 [32 / (18 x 16)]

= log27­ (1/9)

= log10 (1/9) / log10­ 27

= log10 3⁻² / log10 3³

= (-2 log10 3) / (3 log10 3)

= -2/3
參考: Adam


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