Answer: The required transformation rule is given by
(x, y) -----> (-x, y).
Step-by-step explanation: We are given to write a rule that describes a transformation across the y-axis.
We know that
if a point is reflected across the y-axis, then the sign before the x co-ordinate changes.
That is, if the point (x, y) is reflected (transformed) across the y-axis, then its new co-ordinates will be
(-x, y).
Thus, the required transformation rule is given by
(x, y) -----> (-x, y).