اگر $A=\left\{ {{10}^{-k}}\left| k\in \mathbb{N} \right. \right\}$ و $B=\left\{ {{10}^{k}}\left| k\in \mathbb{N} \right. \right\}$ باشد. مجموعهی $A\bigcup B$ برابر کدام گزینه است؟
1 )
$\left\{ \pm {{10}^{\pm k}}\left| k\in \mathbb{N} \right. \right\}$
2 )
$\left\{ \pm {{10}^{-k}}\left| k\in \mathbb{N} \right. \right\}$
$\left\{ {{10}^{\pm k}}\left| k\in \mathbb{N} \right. \right\}$
4 )
$\left\{ \pm {{10}^{k}}\left| k\in \mathbb{N} \right. \right\}$