Find the general term, in simplified form...

$\displaystyle (x^2-x)^10 $ (exponent 10) and $\displaystyle (a-1/a)^13$ (exponent 13)

for the first one I got an answer of $\displaystyle (10 r) x^20-r $ (exponent 20) and the second one is $\displaystyle (13 r) a^13-2r$ (exponent 13) ....but what I can't get is the $\displaystyle (-1)^r$ included for both of the answers