Example 69

$\;\;\;(2l^{4} - k^{4})^2$

$=(A - B)^2 \text{, where } A = 2l^{4} \text{ and } B = k^{4} $

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

$=(2l^{4})^2 - 2(2l^{4})(k^{4}) + (k^{4})^2 $

$=4l^{8} - 4k^{4}l^{4} +k^{8} $