Example 3

$\;\;\;(p + 5q)^2$

$=(A + B)^2 \text{, where } A = p \text{ and } B = 5q $

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

$=(p)^2 + 2(p)(5q) + (5q)^2 $

$=p^{2} + 10pq +25q^{2} $