Answer:
A' (-1,4)
B' (-4,3)
C' (-2,1)
Explanation:
When reflecting a point across the y-axis, the x-coordinate changes signs, and the y-coordinate stays the same. The rule for a reflection across the y-axis is (x,y) -> (-x,y). For example, if we flip the coordinates (1,4) across the y-axis, new the coordinates are (-1,4).