Example 14

$\;\;\;(10a^{5} + 9b)^2$

$=(A + B)^2 \text{, where } A = 10a^{5} \text{ and } B = 9b $

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

$=(10a^{5})^2 + 2(10a^{5})(9b) + (9b)^2 $

$=100a^{10} + 180a^{5}b +81b^{2} $