Example 50

$\;\;\;(11a - 3b)^2$

$=(A - B)^2 \text{, where } A = 11a \text{ and } B = 3b $

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

$=(11a)^2 - 2(11a)(3b) + (3b)^2 $

$=121a^{2} - 66ab +9b^{2} $