(2(log1/2x) 3)((log1/2x) 3)<=0-3<=log1/2x<=-3/2换底公式 log1/2x=log(2)x/log2(1/2)=-log（2）x∴3/2<=log(2)x<=3令y=log（2）x 3/2<=y<=3f(x)=(y-1)(y-3)=y²-4y 3=（y-2）²-1y=2时，有最小值-1y=3时，有最大值0
