因式分解：1.a²-2a2.（a+2)(a-2)+3a 3.a²-4 4.2a²-18

因式分解：1.a²-2a2.（a+2)(a-2)+3a 3.a²-4 4.2a²-18
因式分解：1.a²-2a2.（a+2)(a-2)+3a 3.a²-4 4.2a²-18

因式分解：1.a²-2a2.（a+2)(a-2)+3a 3.a²-4 4.2a²-18
a²-2a
=a(a-2)
（a+2)(a-2)+3a
=a^2-4+3a
=(a-1)(a+4)
a²-4
=(a+2)(a-2)
2a²-18
=2(a^2-9)
=2(a+3)(a-3)

1. a²-2a

=a(a-2)

2.（a+2)(a-2)+3a 

=a²-4+3a

=(a+4)(a-1)

3.a²-4 

=(a+2)(a-2)

4.2a²-18

=2(a²-9)
=2(a+3)(a-3)