Functions are a specific types of relations, where for every "input" there is onli one observation our "output", the "input" / X-value is the independent value and the "output" / Y-value is the dependent value, meaning that it varies alongside X.
First organize the pairs in a table:
As you can se for the input X=-8 there are two outputs Y=8 and Y= 6.
Since the function, by definition only has one value of Y per value of X, this relation is not a function.