f(x)是偶函数
∴ f(log2 x)=f(-|log2 x|),f(1/2)=f(-1/2)
∴ f(log2 x)>0
即 f(-|log2 x|)>f(-1/2)
f(x)在(-∞,0)上是减函数
∴ -|log2 x|1/2
∴ log2(x)>1/2或log2(x)log2(√2)或 log2(x)√2或0