Example 46

$\;\;\;(2x - y)^2$

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

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

$=(2x)^2 - 2(2x)(y) + (y)^2 $

$=4x^{2} - 4xy +y^{2} $