If f (k) = k / (1 - k), then f (1 / k) f (-k) = ?
回答 (2)
2008-01-19 9:46 pm
✔ 最佳答案
= [ (1/k) / (1-1/k) ] x [ -k/(1+k) ]= 1 / [ k(1-1/k) ] x [ -k/(1+k) ]
= 1/(k-1) x -k/(1+k)
= -k / (k-1)(k+1)
= -k / k^2 -1
2008-01-19 9:51 pm
f (1 / k)
= (1 / k) / ( 1 - 1 / k)
= 1 / (k - 1)
f (-k)
= -k / (1 + k)
∴ f (1 / k) x f (-k)
= -k / (1 + k) x 1 / (k - 1)
= k / ((1 - k) (1 + k))
= (1 / k) / ( 1 - 1 / k)
= 1 / (k - 1)
f (-k)
= -k / (1 + k)
∴ f (1 / k) x f (-k)
= -k / (1 + k) x 1 / (k - 1)
= k / ((1 - k) (1 + k))
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https://hk.answers.yahoo.com/question/index?qid=20080119000051KK01612