数列敛散性
如果an或cn收敛,则bn收敛,否则可取an=n,cn=n+1/n,bn=n+1/2n,显然满足题意,但bn发散.设an收敛于a,由|bn-a|≤|bn-an|+|an-a|≤|cn-an|+|an-a|再由lim(cn-an)=0和liman=a得bn→a