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

题目

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

答案

(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