(1)1/4≤x≤4
log2(1/4)=12 log2(4)=2
所以t∈(-2,2)
(2)f(x)=(log4+logx)(log2+logx)
(底数2我就不写了~)
令t=logx
则f(x)=(t+2)(t+1)
=t^2+3t+2
=(t+3/2)^2-1/4
当t=-3/2时,取得最小值,为-1/4
当t=2时,取得最大值,为12
(1)1/4≤x≤4
log2(1/4)=12 log2(4)=2
所以t∈(-2,2)
(2)f(x)=(log4+logx)(log2+logx)
(底数2我就不写了~)
令t=logx
则f(x)=(t+2)(t+1)
=t^2+3t+2
=(t+3/2)^2-1/4
当t=-3/2时,取得最小值,为-1/4
当t=2时,取得最大值,为12