Example 83

$\;\;\;(p + 5q)(p - 5q)$

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

$=A^2-B^2$

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

$=p^{2} - 25q^{2} $