$\Big(x^2-\dfrac{2}{x^3}\Big)^{2011}$
$=\sum\limits_{k=0}^{2011}C_{2011}^k.x^{4022-2k}.(-2)^k.\dfrac{1}{x^{3k}}$
$=\sum\limits_{k=0}^{2011}C_{2011}^k.(-2)^k.x^{4022-5k}$
$\Rightarrow 4022-5k=2012$
$\Leftrightarrow k=402$
Vậy hệ số là:
$C_{2011}^{402}.(-2)^{402}$
$=C_{2011}^{402}.2^{402}$