Is { (8,5), (7,5), (6,2), (8,3), (1,-4), (-4,6) } a function? why?

No. because you have One domain value that says 2 different numbers

Step-by-step explanation:

functions cannot have f (8) = 5 and f (8) = 3 at the same time

because then f (8) is not equal to f (8) it cannot be confusing.