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log問題

想問下

4[5^2(x+2)]=3-25(5^x) 呢條是點計?
我只係識將[5^2(x+2)]變左做5^(2x+4)....跟住就唔識做了,謝解答...

Let y = 5^(x+2)
   4[5^2(x+2)]=3-25(5^x)
  4 [ (5^(x+2))(5^(x+2)) ] + 5^2 (5^x) - 3 = 0
  4 [ (5^(x+2) ]^2 +  5^(x+2) - 3 = 0

   4y^2 + y - 3 = 0
   (4y - 3) ( y + 1) = 0
   y = 3/4   or y = -1
5^(x+2) = 3/4  or 5^(x+2)  = -1  (rejected)

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(請繼續計落去)

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