If you do not know the change of base relation then stop doing this and go back and learn the propoerties of the functions.
Also always specify the base of a if it is not a natural logarithm. You teacher may think they are teaching a convention when they tell you denotes and denotes but its not a universal convention.
Ok I done that and checked the answer and it was my answer would have been .
The next part of the question is:
Assuming the validity of the process, differentiate as given to show that as far as the term in , .