Example 4

$\;\;\;(6a + 5b)^2$

$=(A + B)^2 \text{, where } A = 6a \text{ and } B = 5b $

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

$=(6a)^2 + 2(6a)(5b) + (5b)^2 $

$=36a^{2} + 60ab +25b^{2} $