You can put this solution on YOUR website! r^3-4r^2-16r+64
group terms:
(r^3-4r^2) - (16r-64)
factor each group:
r^2(r-4) - 16(r-4)
(r-4)(r^2-16)
but, we can rewrite the second term as:
(r-4)(r^2-4^2) (difference of squares)
(r-4)(r-4)(r+4)
or
(r+4)(r-4)^2
