a＞1,b＞1,得 log2(a)＞0,log2(b)＞0
log2(a)*log(b)=64,则 log2(ab)=log2(a)+log(b)≥2根号64=16
当且仅当log2(a)=log2(b)=8 即 a=b=256 时,取最小值16