y=x+2
------
x2-1

If you mean 2 different functions, (x + 2) and (x^2 -1), they being defined for all real numbers, their domain is (-infinity, +infinity).


If you mean y = (x + 2)/(x^2 -1)


The function is not defined when the denominator is zero,
i.e. when x^2 = 1

or x = 1, -1


The domain is all real numbers except 1 and -1.

Hence domain cannot be written as a single interval, but as a union of the following:

(-infinity, -1), (-1, 1), (1, infinity)

All being open intervals. (hence -1, 1 are not included in these intervals)

Thanks, it was the second I just get confused on the actual definition of domain, I think it's finding what doesn't come out to zero, but I'm probably wrong.

f(x)= 3x-1