To be a function every x should have only one y-value.
a. (0,0), (1,1), (2,2), (3,3), (4,4) - We do not see repeating values of x, so it is a function
b. (0,8), (1,6), (2,4), (3,2), (4,0)- We do not see repeating values of x, so it is a function
c. (3,0), (3,1), (3,2), (3,3), (3,4) - We see repeating value of x, that means that one value of x corresponds many values of y , so it is not a function.
