Example 23

$\;\;\;(7 + 5x^{4}y)^2$

$=(A + B)^2 \text{, where } A = 7 \text{ and } B = 5x^{4}y $

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

$=(7)^2 + 2(7)(5x^{4}y) + (5x^{4}y)^2 $

$=49 + 70x^{4}y +25x^{8}y^{2} $