How do we identify one-to-one fuctions?

A function is said to be one-to-one, if for each element of the range, there is a unique element of the domain. (for every y there is one and only one value x). if whenever
f (a) = f (b) then a = b.

Lets try out these problems,

1. {(3,2), (1,7) , (0,2)} this is a function but it is not a one-to-one function.
2. {(2,1) , (4,2) , (1,4)} this is a function and it is also a one-to-one function.

(regentsprep.org)

"One-to-One"

NOT "One-to-One"