the question posed is
Given that for all values of , find the value of and the value of .
is this correct?
and solving for b
and expanding the RHS
Your solution is correct, however there is a much easier way of getting to it:
Simply look at the equation when (you can do this since you are told that it holds for any
Then, you get: :
This gives us two possible solutions, however is obviously wrong! so we are left with