Subject: Domain and Range FROM: Stacey Hutchison LEVEL: Secondary school (10-12) TEACHER What is the domain of: f(x) = -1/(x + 4) I have looked at this question and I think that the domain would be that x cannot = 4, XER. Am I even close to the right answer? Hi Stacey, To find the domain of a function you need to ask yourself the question "what x-values am I allowed to use". It's often easier to look at a function and ask yourself "what x-values am I NOT allowed to use". In this case, since division is involved, you know you cannot divide by zero. What x-value would lead to a division of zero? In this case x=-4. Hence the domain is any real number, EXCEPT x=-4. Similarily, the domain of f(x) = -x / (x+1)(x-2) would be any x-value except x=-1 and x=2. If you have a function with an even root in it, remember that you cannot take an even root of a negative number. As a result, in a function such as f(x) = sqrt(x-1) only x-values greater than x=1 are allowed, hence the domain is all x>1. Hope this helps, Patrick Go to Math Central