Answer: (-∞,0)U(0,-∞)
Explanation:
since the denominator of a fraction cannot be 0 we have to find every x value that causes it to be 0
1 - e^x = 0
add e^x to both sides
1 = e^x
since anything to the power of 0 is 1, the only thing x cannot be is 0
1 = e^0
put into interval notation
(-∞,0)U(0,∞)