F.5 Maths! prove log ..

呢題係prove或是solve x?

2009-05-17 17:59:21 補充：
我當呢題係solve x去計:

圖片參考：http://i707.photobucket.com/albums/ww74/stevieg90/03-14.gif

log( 2做底 ) [(4^x-2)-12] </= x-2

Log2[(4x-2)-12]<=x-2
Log2[(4x-2)-12]<= Log22 x-2
4 x-2-12<=2 x-2
(2 x-2)2-12<=2 x-2
(2 x-2)2-2 x-2-12<=0
(2 x-2-4)( 2 x-2 +3) <=0
(2 x-2-4) <=0 或 ( 2 x-2 +3) <=0
2 x-2<=4 或 2 x-2<=-3 (捨去)
2 x-2<=22
因此, x<=4
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