F.3 math factorization HELP!!!

u^3+8-(u+2)^2
=(u+2)(u^2-2u+4)-(u+2)^2
=(u+2)(u^2-2u+4-(u+2))
=(u+2)(u^2-3u+6)

2011-10-23 20:08:51 補充：
don't del this question plz

2011-10-23 20:41:58 補充：
correction:
because x^3+y^3=(x^2 - xy + y^2)(x + y)
thus
u^3+8-(u+2)^2
=u^3+2^3-(u+2)^2
=(u^2-2u+4)(u+2)-(u+2)^2
=(u+2)(u^2-2u+4-(u+2))
=(u+2)(u^2-2u+4-u-2)
=(u+2)(u^2-3u+2)
=(u+2)(u-1)(u-2)

2011-10-23 20:50:41 補充：
don't del this question plz

u^3+8-(u+2)^2
=(u+2)(u^3-2u+4)-(u+2)^2
=(u+2)(u^2+2u+4-u-2)
=(u+2)(u^2-3u+2)
=(u+2)(u-1)(u-2)