Example 78

$\;\;\;(p^{9}q^{10} - 2)^2$

$=(A - B)^2 \text{, where } A = p^{9}q^{10} \text{ and } B = 2 $

$=A^2 - 2AB + B^2$

$=(p^{9}q^{10})^2 - 2(p^{9}q^{10})(2) + (2)^2 $

$=p^{18}q^{20} - 4p^{9}q^{10} +4 $