Answer:
a=2
Step-by-step explanation:
Please see attached picture for full solution.
Method 1: Substitute x with another number, other than the numbers that you have already tried. Zero is a good number to work with :)
Then, subst. the values of b and c which you have already found into the equation. Then simplify to arrive at your answer.
Method 2: Notice that when you expand the right hand side, only a(x)() can give you a term. Hence, compare the coefficients of on both sides. This method is quite safe since the value of a won't be affected in case the value of b and c is wrong.