Is each relation a function ...?

Question

{(1,-2)(-2,0)(-1,2)(1,3)}

and

{(1,1)(2,2)(3,5)(4,10)(5,15)}

how can you tell if it is a function or not

Answer 1

1,-2)(-2,0)(-1,2)(1,3)}

Not a function because

1------>-2

-2------>0

-1------>2

1------->3

here, for the input '1' there is two output '-2'a and '3'

where as f(x)=x is a function if for any value of 'x' there is a unique value of y.

second one is a function, you make it out why so?