Other two names for ray AB is
Reflection of f, over line CG
Perpendicular of line CG pointing downwards
What is reflection of ray f
When ray f is reflected over line CG, the line fo reflection is line CG and the mirror image will be a flip of ray f
This is shown s ray AB in the figure.
Ray AB and ray F are two rays opposing each other, they are both perpendicular to line CG. Ray f is pointing upwards, while ray AB i pointing downwards