方程x²+2(a-1)x+1=0有解时,
判别式△=4(a-1)²-4≥0
(a-1)² -1≥0
(a-1+1)(a-1-1) ≥0
a(a-2) ≥0
∴a≤0且a≤2,或a≥0且a≥2,
得a≤0,或a≥2