\displaystyle \vert \frac{1}{b_{n}}-\frac{1}{b} \vert = \frac{\vert b - b_{n} \vert }{\vert b_{n}\vert \vert b \vert } < \frac{\epsilon {\vert b \vert}^{2}}{2} \cdot \frac{2}{ {\vert b \vert}^{2}} = \epsilon{