(3a+1)(3a-1)+3(a+2)(a-2)-(7a+1)(a-1)重点(7a+1)(a-1)

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(3a+1)(3a-1)+3(a+2)(a-2)-(7a+1)(a-1)重点(7a+1)(a-1)
(3a+1)(3a-1)+3(a+2)(a-2)-(7a+1)(a-1)
重点(7a+1)(a-1)

(3a+1)(3a-1)+3(a+2)(a-2)-(7a+1)(a-1)重点(7a+1)(a-1)
(7a+1)(a-1)不能利用公式.
原式=9a^2-1+3a^2-12-7a^2+6a+1=5a^2+6a-12

=(3a+1)(3a-1)+3(a+2)(a-2)-(6a+a+1)(a-1)
=(3a+1)(3a-1)+3(a+2)(a-2)-(a+1)(a-1)-6a(a-1)
下面自己算了,应该乘乘,加加,减减就好了