1、f（x）=2(log2(x))^2+2a*log2(1/x)+b
=2(log2(x))^2-2a*log2(x)+b
=2[log2(x)-a/2]^2+b-a^2/2
当log2(x)=a/2时,有最小值b-a^2/2
∴log2(1/2)=a/2；b-a^2/2=-8
解得a=-2,b=-6
2、f(x)=2[log2(x)+1]^2-8＞0
[log2(x)+1]^2-4＞0
[log2(x)+1+2][log2(x)+1-2]＞0
log2(x)＞1或＜-3
x＞2或0＜x＜1/8
3、A交B=空集
两种可能：
一、t+1/2≤0
解得,t≤-1/2
二、t-1/2≥1/8且t+1/2≤2
解得,5/8≤t≤3/2