Consider any point P(x, y) in the coordinate axis.
The reflection of this point across the y-axis is the point P'(-x, y).
(x, y) and (-x, y) are the 'mirror' images of each other, with the y'axis as the 'mirror'.
For example the coordinates of the image of P(4, 13) after the reflection across the y-axis is P'(-4, 13)
or, if P(-5, -9), then P'(5, -9)
Answer: if coordinates of V are (h, k), coordinates of V' are (-h, k)