f'(x)=-2x+a-1/x=-(2x^2-ax+1)/x
(1):在(0,0.5)递减,2x^2-ax+1≥0,a≤(2x+1/x)的最小值,最小值在x=0时为0,a≤0
(2):是在(1)的条件下吗?不然没法做啊