Based on the fact that the right line is a reflection across the y-axis, the lines are the same, they are just in a different position.
What is a Reflection?
This refers to the rigid transformation type that is used to represent an image and does not change its size or length of it.
With this understanding, we can see that the pre-image and the image in a rigid transformation are congruent which makes the lines to be the same, even if they are in a different position.
