There need to be restrictions generally so as for the expression to be legit. First of all, it must be $1+x \neq 0$ since it is the denomimator of a fraction. Secondly, it's a quantity below of a root, so it also must be positive.
I am mentioning these because despite the power rule being correct, the expression wouldn't be legit for any $x$ or $b$ as you mentioned.
There need to be restrictions generally so as for the expression to be legit. First of all, it must be $1+x \neq 0$ since it is the denomimator of a fraction. Secondly, it's a quantity below of a root, so it also must be positive.
I am mentioning these because despite the power rule being correct, the expression wouldn't be legit for any $x$ or $b$ as you mentioned.