x²-(a-1)x-a²≤0
解方程x²-(a-1)x-a²=0,得
x=[a-1±√(5a²-2a+1)]/2
[a-1-√(5a²-2a+1)]/2≤x≤[a-1+√(5a²-2a+1)]/2
|x|≤1
-1≤x≤1
∴[a-1-√(5a²-2a+1)]/2≥-1;[a-1+√(5a²-2a+1)]/2≤1
a²-a≤0,2a²+2a+5≥0
解得,0≤a≤1