The problem you are talking about belongs to the derivative problem in high numbers.

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.