y=x²+bx-1
x=3 y=2
2=9+3b-1
b=-2
y=x²-2x-1
(2)y=x²-2x-1≥2
x²-2x-3≥0
(x-3)(x+1)≥0
x≥3 x≤-1
x>0
∴x≥3