(1)当x∈(0,x1)时,g(x)>0,从而x0,所以x1>f(x)
(2)由已知x0=-b/2a,由x1+x2=(1-b)/a得x1+b/a=1/a-x2>0,所以x1+b/a>0.即x1>-b/a,则x1/2>-b/2a=x0
,得证