# Math Help - factorizing ehh :(

1. ## factorizing ehh :(

hey guys, just doin a lil study..im a little confused about these questions.

factor these two questions:

1)
$
81x^2 - 16y^2
$

2)
$
(y+3)^3 + 8
$

any ideas?

2. 1. This is a product of 2 squares .

$

81x^2 - 16y^2 = (9x - 4y)(9x + 4y)
$

2. Multiply out the brackets and add the 8. Then factorise:

$

(y+3)^3 + 8 = y^3 + 9y^2 + 27y + 35 = (y+5)(y^2+4y+7)
$

Hope this helps.

3. Considering that you seem to be focusing on difference of squares, sum and difference of cubes, the intention is probably, for #2, that you recognize that $(y+3)^3 + 8$ is a difference of cubes and use that formula (where $a = (y + 3), b = 2$). You can do it the other way - multiply it all out - as well.