Answer
2(y)(3$x^2$ + $y^2$)
Work Step by Step
$(x+y)^3$ - $(x-y)^3$
Now, $a^3$ - $b^3$ = (a-b)($a^2$ + $b^2$ + ab)
and a = x+y , b = x-y
Which implies,
= ((x+y) - (x-y))($(x+y)^2$ + $(x-y)^2$ + (x+y)(x-y))
Now, $(a + b)^2$ = $a^2$ + $b^2$ + 2ab
and a = x , b = y
Now, $(a - b)^2$ = $a^2$ + $b^2$ - 2ab
and a = x , b = y
Now, $a^2$ - $b^2$ = (a+b)(a-b)
and a = x , b = y
Which implies,
= 2(y)(($x^2$ + $y^2$ + 2xy) + ($x^2$ + $y^2$ - 2xy) + ($x^2$ - $y^2$))
= 2(y)(3$x^2$ + $y^2$)
which is the answer