My opinion is as follows-
1, derivative formula: y = u/v, y' = (u' v-uv')/v 2.
2. According to the above formula, there are:
f'(x)=(a+x)'? *( 1+x)-(a+x)*( 1+x)' /( 1+x)^2
=( 1+x)-(a+x)/( 1+x)^2
=( 1-a)/( 1+x)^2
The above answers are for your reference.