The option that best describes the relationship between the x-axis and the line connecting P to P′ is: They are perpendicular to each other.
How to Interpret the Transformation?
There are different types of transformation such as:
Reflection
Rotation
Dilation
Translation
Now, after a reflection over the x-axis, the image will just be a mirrored one and as such the line joining P and P' will be perpendicular to the X axis.