x属于[1,2]
f(x)=ax^2-x+2a-1=a(x-1/2a)^2+2a-1-1/4a
a>0时,
(1)顶点横坐标在[1,2]
1≤1/2a≤2
1/4≤a≤1/2
g(a)=2a-1-1/4a=(8a^2-4a-1)/4a
(2)顶点横坐标2
1/2a>2
0
x属于[1,2]
f(x)=ax^2-x+2a-1=a(x-1/2a)^2+2a-1-1/4a
a>0时,
(1)顶点横坐标在[1,2]
1≤1/2a≤2
1/4≤a≤1/2
g(a)=2a-1-1/4a=(8a^2-4a-1)/4a
(2)顶点横坐标2
1/2a>2
0