Question

how can you make this a non- function.f(x){(1,-8),(3,-4),(5,0),(9,4),(10,-2)

Answer 1

If the relation contains elements where a single value in the domain maps to two or more points in the image, the relation is not a function.

For example:
R1:{(1,2),(2,3),(3,5),(6,5)}
is a function, while
R2:{(1,2),(1,3),(3,4)}
is not.