Special Products Rule 7

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Expand $(7x - y)(49x^{2} + 7xy +y^{2})$

**Answer**

$\;\;\;(7x - y)(49x^{2} + 7xy +y^{2})$

$=(7x - y)((7x)^2 + (7x)(y) + (y)^2) $

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

$=A^3 - B^3 $

$=(7x)^3 - (y)^3 $

$=343x^{3} - y^{3} $