Example 54

$\;\;\;(10p - 3q)^2$

$=(A - B)^2 \text{, where } A = 10p \text{ and } B = 3q $

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

$=(10p)^2 - 2(10p)(3q) + (3q)^2 $

$=100p^{2} - 60pq +9q^{2} $