[tex]A=\Big\{\text{x}\in\mathbb_{N}$ $ \Big|$ $\text{x}\ \textless \ 100 $ $ $ si $ $ $ \text{x} $ $\vdots$ $ 11}\Big\} \\ \\ \\ \Rightarrow \left\{ \begin{array}{c} \text{x} \in M_{11} \\\text{x} \ \textless \ 100 \end{array} \right \Rightarrow\left\{ \begin{array}{c} \text{x} \in \Big\{11,22,33,44,...,\infty\Big\} \\\text{x} \ \textless \ 100\quad \quad \quad \quad\quad \quad \quad $ $ $ $ \end{array} \right |\Rightarrow \\ \\ \\[/tex]
[tex] \Rightarrow \text{x} \in \Big\{11,22,33,44,55,66,77,88,99\Big\},\quad$dar, x$ $ \in \mathbb_{N} \Rightarrow \\ $ $\\ \\ \Rightarrow \boxed{A = \Big\{11,22,33,44,55,66,77,88,99\Big\}}[/tex]
