3a1+3d=-3,a1(a1+d)(a1+2d)=8
问题描述：
3a1+3d=-3,a1(a1+d)(a1+2d)=8
答
3a1+3d=-3,①
a1(a1+d)(a1+2d)=8 ②
①==> a1+d=-1 ③ 代入②
a1(a1+2d)=-8 ④
又 ③==> a1=-d-1代入 ④
∴（-d-1)(-1+d)=-8
∴ d²-1=8,d²=9
∴d=3,a1=-4或d=-3,a1=2