(1)f(x)ax+1>0,ax>-1,a>0,x>-1/a①x>0,②①②之交为②。(ax+1)/x<(a-4)x+2a-5,③由②③，ax+1<(a-4)x^2+(2a-5)x,整理得(a-4)x^2+(a-5)x-1>0,(x-1)[(a-4)x+1]>0,a=4时x>1;a>4时x>1或x<-1/（a-4）;0与②求交集得a>=4时x>1;0
