اگر $f=\left\{ (1,2),(-2,3),(\frac{1}{2},1) \right\}$. و $g=\left\{ (\frac{1}{2},3),(3,-2),(1,5) \right\}$ ، مجموعهٔ ${{D}_{f+g}}$ کدام است؟
1 )
$\left\{ \frac{1}{2},3,1,-2 \right\}$
$\left\{ \frac{1}{2},1 \right\}$
3 )
$\left\{ 3 \right\}$
4 )
$\left\{ \frac{1}{2},3 \right\}$