Question 350620: I just took a math test and wanted to see if I had done this right.
I determined that each side of this expression was a cube. 8^3=512, 9^3=729. So I answered: (8y x 8y x 8y)-(9 x 9 x 9). Was this correct? Answer by nerdybill(7003) (Show Source):
You can put this solution on YOUR website! Hate to be a bearer of bad news but you didn't get it right.
can be rewritten (as you say) as:
At this point you have a "difference of cubes" -- a special case for factoring:
a^3 – b^3 = (a – b)(a^2 + ab + b^2)
which then gives you:
(8y - 9)((8y)^2 + (8y)(9) + 9^2)
(8y - 9)(64y^2 + 72y + 81)