Show that the function `f: ZvecZ` defined by `f(x)=x^2+x` for all `x in Z ,` is a many one function.

Explanation

Let `x, y in Z` such that `f(x)=f(y)`
`

Rightarrow x^{2}+x=y^{2}+y `
`
Rightarrow x^{2}-y^{2}+x-y=0 `
`
Rightarrow(x-y)(x+y+1)=0 `
`
Rightarrow x=y { or } x=-y-1`



...