令,2^x=m,m属于[1/2,2],有
X=log2(m),-1≤x≤1.
-1≤log2(m)≤1,1/2≤m≤2.有
1/2≤log2(x)≤2,
√2≤x≤4.
则f(log2x)的定义域为√2≤x≤4.