x^2+(a-1)x+1>0
[x+(a-1)/2]^2-(a-1)^2/4+1>0
∵ [x+(a-1)/2]^2 恒大于等于0
∴ 1-(a-1)^2/4>0
1>(a-1)^2/4
2>(a-1)>-2
∴ -1