f(x)=alnx+(a+1)/2·x+1,x＞0f'(x)=a/x+(a+1)x=[(a+1)x+a]/x(1) a=-1,f'(x)=-1/x＜0,f(x)在(0,+∞)单调减；(2) a＜-1,(a+1)x+a＜0恒成立,f'(x)＜0,f(x)在(0,+∞)单调减；(3) -1＜a＜0,令f'(x)=0,即 考虑到x＞0,解得x...