x1x2 = a^2-7a-4
x1+x2 =-2(a-1)
x1x2-3x1-3x2-2 =x1x2 - 3(x1 + x2 ) -2
=a^2-7a-4 +6(a-1) -2 =a^2 -a -12=0
解得 a=4,-3
a= - 3 代入方程,△x1x2 = a^2-7a-4x1+x2 =-2(a-1)这两个怎么来的，真不会、这是根与系数的关系，就是韦达定理，你们没学吗？ax^2 +bx+c=0有两根x1,x2则x1x2=c/a x1+x2 =-b/a额、没学，不过现在懂了，谢谢