Example 72

$\;\;\;(k^{2}l^{3} - 7)^2$

$=(A - B)^2 \text{, where } A = k^{2}l^{3} \text{ and } B = 7 $

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

$=(k^{2}l^{3})^2 - 2(k^{2}l^{3})(7) + (7)^2 $

$=k^{4}l^{6} - 14k^{2}l^{3} +49 $