提示:\[\sum\limits_{k = 0}^n {\left| {{b_{n - k}}} \right|} = {B_n} \to B\]
提示二:\[B\sum\limits_{n = N}^\infty {\left| {{a_n}} \right|} - \sum\limits_{n = N}^\infty {\left( {\left| {{a_n}} \right|{B_n}} \right)} = \sum\limits_{n = N}^\infty {\left| {{a_n}} \right|\left( {B - {B_n}} \right)} \to 0\] |