x = \sum\limits_{i = 1}^n {\lambda _i {\bf e}_i } \Rightarrow \left\| {Ax} \right\| = \left\| {\sum\limits_{i = 1}^n {\lambda _i A{\bf e}_i } } \right\| \le \sum\limits_{i = 1}^n {\left| {\lambda _i } \right|\left\| {A{\bf e}_i } \right\|}