The y coordinate will stay the same. The x coordinate will flip from positive to negative, or vice versa.
Some examples:
(1,2) ----> (-1,2)
(-3,4) ----> (3,4)
(-1.2, 8) ----> (1.2, 8)
The general rule is
(x,y) ----> (-x, y)
indicating that only the x coordinate undergoes a change