急! F5 about equations 1Cq01

2012-08-16 3:00 am

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回答 (2)

2012-08-16 6:57 am
✔ 最佳答案
因為log對負數是沒有意義的。因此對於有log的方程﹐解題後需要將根代回原方程檢查會不會出現負數的log﹐有則要捨去

17(a) 對x = 2, log(2 - 4) =log (-2) 因此捨去

(b) 同理對x = 1.4768﹐log(1.468^2 - 9) = log(-6.844976) 因此捨去

(c) 事實上x = -13.4是沒有問題的

因為4 + (-13.4)^2 = 183.56﹐7 - (-13.4) = 20.4 都是正數。
2012-08-16 3:14 am
If 2 and 1.468 are sub. into the questions, there will be log negative no., which is impossible. I think you can now understand what's wrong with your ans in Q3.


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