Suppose the domain of f is (-1,1). Define the function j by j(x)=f(1/x). What is the domain of j?

  We have that the domain of f(x) is

- 1  < x <  1

Then the domain of  f ( 1/x)  is

-1  <  1/x  <  1    

-1 < 1/x       this will be true when  x < -1  and  x > 0

And

1/x < 1       this will be true when      x > 1

So.....we need to take the most restrictive interval(s)  in our solution

So the domain of  f (1/x)  is    ( - inf, -1)  U ( 1, inf )  = domain of j(x)