据题意：(2-x)^2-(a-1)(2-x)+5=(2+x)^2-(a-1)(2+x)+5
-4x-2(a-1)+(a-1)x=4x-2(a-1)-(a-1)x
2(a-1)x=8x
（a-1)=4
a=5
(2)
∵f(x)在区间（1/2,1）上是增函数
∴f(1)-f(1/2)＞0
1-(a-1)+5-[(1/2)^2-(a-1)*(1/2)+5]＞0
1-(a-1)+5-1/4+1/2(a-1)-5＞0
3/4-1/2*(a-1）＞0
3＞2（a-1)...(1)
f(2)=4-2(a-1)+5=9-2(a-1)...(2)
由（1）和（2）得f(2)＞6