√2＝2^(1/2)＝4^(1/4)
8＝2^3＝4^(3/2)
因此 4^(1/4)≤x≤4^(3/2)
∴1/4≤log4x≤3/2
∴-3/2≤2(log4x-1)≤1,即-3/2≤f(x)≤1