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標題:

測驗溫習唔識!!

發問:

〖423〗^x=27,〖47〗^y=27,則1/x-1/y=?

 

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最佳解答:

423^x = 27 423 = 27^(1/x) 47^y = 27 47 = 27^(1/y) [27^(1/x)] / [27^(1/y)] = 423 / 47 27^ (1/x - 1/y) = 9 3^ [3(1/x - 1/y)] = 32 So, 3(1/x - 1/y) = 2 1/x - 1/y = 2/3.

其他解答:

xlog423 = log 27 ylog47 = log27 1/x-1/y = log 423/log 27-log47/log 27 = (log 423-log47)/log27 = [log(47* 9)-log47]/log (3*9) =[log 47+log 9 -log 47]/ log (3*9) =log 9/(log 3 + log 9) =2/38758B59A7FA1EEA7
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