几道因式分解（一题10分）

（1）a^3-3a^2+3a-1 =(a-1)^3
(2)2a^5+4a^4*b+16a^2*b^3+32a*b^4
=2a(a^4+2a^3b+8ab^3+16b^4)
=2a(a+2b)(a^3+8b^3)
=2a(a+2b)^2(a^2-12ab^2-6a^2b+4b^2)
(3)a^2-2a(b-c)+(c-b)^2
=(a-b+c)^2
(4)(x+y)^2-22x-22y+21
=(x+y)^2-22(x+y)+21
=(x+y-21)(x+y-1)

4) 原式=（x+y)^2 -22(x+y)+21= （x+y-1)(x+y-21)

^