(1)f(0)=1c=1(2分)
y=-2x+1
y=a x 2 +bx+1 ax 2+(b+2)x=0有等根(5分)
b=-2(7分)
(2)f(x)=ax 2-2x+1=a(x-
1
a ) 2+1-
1
a (8分)
1
3 ≤a≤1∴1≤
1
a ≤3恒有N(a)=1-
1
a (10分)
当1≤
1
a ≤2即
1
2 ≤a≤1时M(a)=9a-5
M(a)-N(a)=2 a=
4±
7
9 a=
4-
7
9 <
1
2 (舍去)(12分)
当2<
1
a ≤3即
1
3 ≤a<
1
2 时M(a)=a-1
M(a)-N(a)=2a=2±
3 >
1
2 都舍去
综上 a=
4+
7
9 (15分)