Example 6

$\;\;\;(7x + 11y)^2$

$=(A + B)^2 \text{, where } A = 7x \text{ and } B = 11y $

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

$=(7x)^2 + 2(7x)(11y) + (11y)^2 $

$=49x^{2} + 154xy +121y^{2} $