Forget the exponents in that step. You have 4 - 2. What's the common factor? 2.
2 is the same as 2^1, so it's written that way in order to emphasize the exponents. That's all. Look at it as simple factoring, with exponents added in after the factoring out.
2 is the same as 2^1, so it's written that way in order to emphasize the exponents. That's all. Look at it as simple factoring, with exponents added in after the factoring out.
