Algebraic representation :
(x, y) => (x, -y)
When you reflect across the x, the x stays the same but the y changes signs.
(1,-2) => (1,2)
(4,-2) => (4,2)
(1,-4) => (1,4)
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
I hope that helps you out!!
Any more questions, please feel free to ask me and I will gladly help you out!!
~Zoey