Example 29

$\;\;\;(6a + b)^2$

$=(A + B)^2 \text{, where } A = 6a \text{ and } B = b $

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

$=(6a)^2 + 2(6a)(b) + (b)^2 $

$=36a^{2} + 12ab +b^{2} $