D = {x ∈ R : x > 0}
1) Considering the function f(x) = -1 -1/x +3 then
2) Examining the Denominator, the values that cause undefinition for this function is when x =0, since 1/0 is undefined.
So we can write out the Domain as:
D= x>0
D = {x ∈ R : x > 0}