Jon P. answered 02/23/15
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First factor out a 2:
2(y3 - 27z3)
Now notice that this is the difference of two cubes -- y and 3z.
The standard factoring for the difference of 2 cubes is:L
a3 - b3 = (a - b)(a2 + ab + b2)
In this case plug y in for a and 3z in for b:
2(y3 - 27z3) =
2(y - 3z)(y2 + y(3z) + (3z)2) =
2(y - 3z)(y2 + 3yz + 9z2)