1.lim an/(an+1) =2 ==>lim (an+1)/an=lim(1+1/an)=1/2 ==>lim 1/an=-1/2==>lim an=-2 ==>lim 2an=-22.lim an/(2n*an)=lim 1/(2n)=0 ==>an远小于 nanlim (2n+1)*an=3 ==>lim 2n*an=3 ==>lim n*an=3/2