因式分解（速！加分）

包你满意~~~~

4x^4-13x^2y^2+9y^4
=(4x^4-4x^2y^2)-(9x^2y^2-9y^4)
=4x^2(x^2-y^2)-9y^2(x^2-y^2)
=(4x^2-9y^2)(x^2-y^2)
=(2x-3y)(2x+3y)(x-y)(x+y)

xy^3+y^2+y-x+1
=(xy³-x)+(y²+y+1)
=x(y³-1)+(y²+y+1)
=x(y-1)(y²+y+1)+(y²+y+1)
=[x(y-1)+1](y²+y+1)
=(xy-x+1)(y²+y+1)

a^2+2ab+2ac-2bc-3b^2
=(a²+2ab+b²)+(2ac-2bc)-4b²
=(a+b)²-4b²+2c(a-b)
=[(a+b)+2b][(a+b)-2b]+2c(a-b)
=(a+3b)(a-b)+2c(a-b)
=(a+3b+2c)(a-b)

(a-1)(a-3)(a-6)(a+2)+56
=[(a-1)(a-3)][(a-6)(a+2)] +56
=[(a²-4a)+3][(a²-4a)-12]+56
=(a²-4a)²-12(a²-4a)+3(a²-4a)-36+56
=(a²-4a)²-9(a²-4a)+20
=[(a²-4a)-5][(a²-4a)-4]
=(a²-4a-5)(a²-4a-4)
=(a-5)(a+1)(a²-4a-4)

1、（n应该是4吧）
(4x^2-9y^2)(x^2-y^2)
=(2x-3y)(2x+3y)(x-y)(x+y)
2、(xy-x+1)(y^2+y+1)
3、(a+3b+2c)(a-b)