Math. Log~~~...

First of all, may I ask where did you get this Q? ( Which book, say )

I ask this Q because:


20000 ( 0.7 )^t - 11000 ( 0.8 )^t = 3000

20 ( 0.7 )^t - 11 ( 0.8 )^t = 3

If you take logarithms, no matter how you change the terms on both sides of the eq., you cannot simplify the power t.

Take the above step for illustration. If you take Log now, the L.H.S. cannot simplify for

log ( x - y ) is not equal to log ( x/y ) or log x - log y

Nothing can be worked out then.

Hope I can help you. You cannot solve using Log.



2011-01-15 11:26:57 補充：
Setvie is right, and that is why I wonder you post a very difficult question which can hardly be found in secondary school textbooks.

If you really want to solve it, we can use Newton's method to get an approximate ans.