| \(\forall \varepsilon >0\quad ,\quad \exists \delta >0\quad s.t.\quad \forall x\in { { R } },\quad 0<\left| x-a \right| <\delta \quad \Rightarrow \quad \left| f\left( x \right) -b \right| <\varepsilon \\ \\ 展開後\quad \quad \forall \varepsilon >0\quad ,\quad \exists \delta >0\quad s.t.\quad \forall x\in { { R } },\quad \begin{cases} x\neq a \\ a-\delta <x<a+\delta \end{cases}\quad \Rightarrow \quad b-\varepsilon <f\left( x \right) <b+\varepsilon \) | | \(\forall \varepsilon >0\quad ,\quad \exists \delta >0\quad s.t.\quad \forall x\in { { R } },\quad 0<\left| x-a \right| <\delta \quad \Rightarrow \quad \left| f\left( x \right) -b \right| <\varepsilon \\ \\ 展開後\quad \quad \forall \varepsilon >0\quad ,\quad \exists \delta >0\quad s.t.\quad \forall x\in { { R } },\quad \begin{cases} x\neq a \\ a-\delta <x<a+\delta \end{cases}\quad \Rightarrow \quad b-\varepsilon <f\left( x \right) <b+\varepsilon \) |