① 16x^2-49y^2
=(4x+7y)(4x-7y)
② 4+12(x-y)+9(x-y)^2
=(3x-3y+2)
③ x^3-9x
=x(x^2-9)
=x(x+3)(x-3)
④ a^4-2a^2 b^2+b^4
=(a^2-b^2)^2
=[(a+b)(a-b)]^2
=(a+b)^2(a-b)^2
⑤ (a^2-a)^2-(a-1)^2
=[a(a-1)]^2-(a-1)^2
=a^2(a-1)^2-(a-1)^2
=(a-1)^2(a^2-1)
=(a-1)^2(a+1)(a-1)
=(a-1)^3(a+1)
⑥ 16x^4-1
=(4x^2+1)(4x^2-1)
=(4x^2+1)(2x+1)(2x-1)
① 3^2004 -4*3^2003 +10*3^2002=_______
=3^2002(3^2-4*3^1+10)
=3^2002(9-12+10)
=7*3^2002
② 3^n+2 -4*3^n+1 +10*3^n=_______
=3^n(9-12+10)
=7*3^n