A reflection through x-axis is the property to get a point and transform it like this:
[tex]\begin{gathered} P\rightarrow P^{\prime} \\ (x,y)\rightarrow(x,-y) \end{gathered}[/tex]If we have point P = (3,4), its reflexion through x-axis will be:
[tex]\begin{gathered} P\rightarrow P^{\prime} \\ (x,y)\rightarrow(x,-y) \\ (3,4)\rightarrow(3,-4) \end{gathered}[/tex]So our final answer will be:
[tex](3,-4)[/tex]