拓跋英虎儿
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f(x)=(log2x-log22)(log2x-log24)
=(log2x-1)( log2x-2)
设t=log2x,根号2≤x≤4,
则1/2≤t≤2.
得f(x)=(t-1)( t -2)
=t^2-3t+2
=(t-3/2)^2-1/4
所以ymin=y(3/2)=-1/4,此时t=3/2,
则log2x=3/2,x=2^(3/2)=2√2.
ymax=y(1/2)=3/4.此时t=1/2,
则log2x=1/2,x=2^(1/2)=√2.
1年前
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