因式分解.1.4a^(n-1)*b^2-16a^(n+1) 2.x^2*y^2-y^4-12xy^2+36y^2 3.x^2-6xy+9y^2-3x+9y+2

1.4a^(n-1)*b^2-16a^(n+1)
=4a^(n-1)(b²-4a²)
=4a^(n-1)(b-2a)(b+2a)
2.x^2*y^2-y^4-12xy^2+36y^2
=y²(x²-y²-12x＋36)
=y²[(x²-12x+36)-y²]
=y²[(x-6)²-y²]
=y²(x-6+y)(x-6-y)
3.x^2-6xy+9y^2-3x+9y+2
=(x-3y)²-3(x-3y)+2
=(x-3y-1)(x-3y-2)3. x^2-6xy+9y^2-3x+9y+2=(x-3y)²-3(x-3y)+2=(x-3y-1)(x-3y-2) 最后一步如何得出的呢？十字相乘法