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)
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a²模厅-2a
=a(a-2)
2.(含岩a+2)(a-2)+3a
=a²-4+3a
=(a+4)(a-1)
3.a²-4
=(a+2)(a-2)
4.2a²谈码御-18
=2(a²-9)
=2(a+3)(a-3)