Question 1040820
The binomial expansion formula as applied in this case is as follows:

{{{sum((matrix(2,1,10,k))*(x^3)^(10-k)*(-x^(-2))^k,k=0, 10)}}}

= {{{sum((-1)^k*(matrix(2,1,10,k))*x^(30-5k),k=0, 10)}}}

==> 30-5k = -5  ==> -5k = -35  ==> k = 7.

Hence the coefficient of {{{x^(-5)}}} is {{{(-1)^7*(matrix(2,1,10,7)) = -120}}}.