Price Is a relation a function?

function

a relation that assigns exactly one output value for each input value

relation

a set of pairs of input and output values

This relation is a function

(-1, 0) (0, 1) (1, 6) (2, 2)

This relation is a function

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

This relation is not a function

(-5, 3) (-5, 2) (3, 7) (3, 8)

This relation is not a function

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

This relation is a function

(1, 2) (3, 4) (4, 5) (5, 2)

This relation is not a function

(1, 3) (2, 4) (2, 5) (3, 9)

if any vertical line crosses a graph in more than one point it is not a function (one x-value has more than one y-value)

What is the vertical line test?

If each number in the domain has an arrow to only one number in the range.

When does the mapping diagram represent a function?