设函数f(x)=log2(4x)*log2(2x) 1/4<=x<=4

(1)若t=log2(x),则t的取值范围(2)求f(x)的最值,并给出最值时对应的x的值
f(x)=log2(4x)*log2(2x)
t=log2(x),
所以f(x)=log2(4x)*log2(2x)
=(log2(x)+log2(4))*(log2(x)+log2(2))
=(t+2)*(t+1)=t^2+3t+2
根据x范围可求t范围,然后可求f(x)范围,同正销时可求对应的x
(1)
1/4<=x<=4
所戚清仔以t属于区间[-2,2]
(2)
f(x)=(t+3/2)^2+2-(3/2)^2=(t+3/2)^2-1/4
所以f(x)>=-1/4
当t=-3/2,即x=2^(-3/2)时,f(x)取得最小值-1/4;
又t属于区间[-2,2],所以(t+3/2)^2<=49/4
f(x)<=49/4-1/4=12
所以t=2,即x=4时,f(x)取得最大值高汪12.
f(x)=log2(4x)*log2(2x)
t=log2(x),
所以f(x)=log2(4x)*log2(2x)
=(log2(x)+log2(4))*(log2(x)+log2(2))
=(t+2)*(t+1)=t^2+3t+2
根据x范围可求t范围,然后高汪可求f(x)范围,同时可求对戚清仔应的x
(1)
1/4<=x<=4
所以t属于区间正销[-2,2]
(2)
f(x)=(t+3/2)^2+2-(3/2)^2=(t+3/2)^2-1/4
所以f(x)>=-1/4
当t=-3/2,即x=2^(-3/2)时,f(x)取得最小值-1/4;
又t属于区间[-2,2],所以(t+3/2)^2<=49/4
f(x)<=49/4-1/4=12
所以t=2,即x=4时,f(x)取得最大值12.
f(x)=log2(4x)*log2(2x)
t=log2(x),
所拦物以f(x)=log2(4x)*log2(2x)
=(log2(x)+log2(4))橘衡稿*(log2(x)+log2(2))
=(t+2)*(t+1)=t*t+3t+2
根据x范围可求t范围,然后可求f(x)范围,圆孝同时可求对应的x
(1)t属闹答于[-2,2]
(2)当x最小=1/4时,f(x)最小=1;当x最液耐慧大=4时,亩裂f(x)最大=64