You could use a simple pencil test to figure it out.
Place a pencil vertically on the paper, and move it left to right or vise-versa
When moving it make sure the pencil doesn't hit two points at once if it does it is not a function, but this is not the case
This is a function
SOH CAH TOA
sin(P) = opp./hyp. = 5/13
tan(T) = opp./adj. = 12/5
cos(T) = adj./hyp. = 5/13