اگر $A=\left\{ \left. x \right|x\in \mathbb{N},x \lt \sqrt{9} \right\}$ و $B=\left\{ \left. \sqrt{x} \right|x\in \mathbb{N},x\le 4 \right\}$ باشند، حاصل $(B-A)\bigcup (A-B)$کدام است؟
1 )
$\left\{ 1,\sqrt{2},\sqrt{3},2 \right\}$
2 )
$\left\{ \sqrt{1},\sqrt{4} \right\}$
$\left\{ \sqrt{2},\sqrt{3} \right\}$
4 )
$\left\{ 1,\sqrt{2} \right\}$