Stick with me here, I don't know how to use something to add an equation in here! 1. The problem statement, all variables and given/known data Find a value of the constant k such that the limit exists: lim x->4 (x^2 - k^2) / (x-4) 3. The attempt at a solution I KNOW the solution is the limit will exist iff k = -4 and k = 4. My problem is - does the numerator have to cancel out the denominator in order for a limit to exist? Or is that just the case here? Cause the solution is: (x-k)(x+k)/(x-4) So the only way for the denominator (x-4) to cancel out would be if k = -4 or 4... so i'm just wondering if that's a general rule? Cheers C.