原式
=3a3+a3-4a-12
=4a3-4a-12
=4a(a2-1)-12
=4a(a+1)(a-1)-12
=4(a-3(a+1)(a-1))
大概就是这样吧,= - =方直接打数字了,请看清...还有中括号用小括号代替了也请看清= - =