Special Products Rule 3

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Expand $(3k + l)(3k - l)$

**Answer**

$\;\;\;(3k + l)(3k - l)$

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

$=A^2-B^2$

$=(3k)^2 - (l)^2 $

$=9k^{2} - l^{2} $