Question

look at this table:
x | y
20 | -16
20 | 1
8 | -16
is this relation a function?
yes no

Explanation:

A function requires each input (x-value) to have exactly one output (y-value). Here, the x-value 20 maps to two different y-values: -16 and 1, violating the function definition.

Answer:

no