when do i know when to set the denominator to 0 when finding the domain of a fraction compared to when i have to find both a positive and a negative number?

Question

f(x)=x+10/x^2-4

Answer 1

You must always set the denominator equal to zero when looking for the domain of a function because if you plug in an x-value that makes your denominator =0, then your function is undefined.
for the function f(x)=x+10/x²-4
you set the denominator=0 so x²-4=0 and solve
x²=4
x=2, or -2 (these values are NOT in your domain)