初二几道因式分解题.1.(a+b)²+6a(a+b)+9a² 2.3y²+9y-12 3.

1.(a+b)²+6a(a+b)+9a²
=(a+b+3a)²
=(4a+b)²
2.3y²+9y-12
=3(y² +3y-4)
=3(y+4)(y-1)
3.(x²+4)²-16x²
=(x² +4)² -(4x)²
=(x² +4x+4)(x² -4x+4)
=(x+2)² (x-2)²
4.3x²-7x-6
=(3x+2)(x-3)