- let f :R{1,-1}-R and f(x)=x/x
^{2}-1.- I am trying to show that the function is surjective,but i have the following questions:
- 1）why we need to divide the case into 2 parts (1):y:R\{0} and (2)y=0 before proving it is surjective.
- 2）and for part(1),why we need to show x:R\{1,-1}. I.e. x isn't equal to +1/-1
- 3）BTW,for the definition of surjective,i don't know the pricinple behind f(x)=y (or why we need to show f(x)=y) (for all y£Y,the exists x£X s.t. y=f(x)

It would be great if you could help me