y=log₂(x/2)×log₂(x/4)
=(log₂x-log₂2)(log₂x-log₂4)
=(log₂x-1)(log₂x-2)
=log₂²x-3log₂x+2
设log₂x=t,
∵x∈[1,8] ∴t∈[0,3]
∴y=t²-3t+2=(t-3/2)²-1/4
∴t=3/2时,y取得最小值-1/4
t=3或0时,y取得最大值2
y=log₂(x/2)×log₂(x/4)
=(log₂x-log₂2)(log₂x-log₂4)
=(log₂x-1)(log₂x-2)
=log₂²x-3log₂x+2
设log₂x=t,
∵x∈[1,8] ∴t∈[0,3]
∴y=t²-3t+2=(t-3/2)²-1/4
∴t=3/2时,y取得最小值-1/4
t=3或0时,y取得最大值2