Example 5

$\;\;\;(12x + 11y)^2$

$=(A + B)^2 \text{, where } A = 12x \text{ and } B = 11y $

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

$=(12x)^2 + 2(12x)(11y) + (11y)^2 $

$=144x^{2} + 264xy +121y^{2} $