ANSWER
The restrictions are
EXPLANATION
We were given the rational function,
The function is defined for all values of a, except
This has become a quadratic trinomial, so we need to split the middle term.
We do that by multiplying the coefficient of which is 5 by the constant term which is 3. This gives us 15.
The factors of 15 that adds up to 16 are 1 and 15.
We use these factors to split the middle term.
We now factor to get,
We factor further to get,
This implies that,
This gives
These are the restrictions.