There is this question asking for a coeffecient of a certain expansion, however I dont seem to be getting the correct answer.
With the expansion of
find the coefficient of
so what I have done is
Meaning
thus
Thus the coefficient of should be
and then it should be multiplied by
thus <- which I think should be the binomial coefficient of
However, i learned that the answer is -12
could anyone tell me where I have went wrong?