已知数列an是等差数列,公差d不等于0,且a1,a2为关于x的方程的x²-a3+a4=0的两根,则an为?

是x²-a3x+a4=0,还是x²-a3+a4=0?
x^2-(a1+2d)x+(a1+3d)=0
将根a1,a1+d分别代入
a1^2-a1^2-2da1+a1+3d=0
(2d-1)a1=3d
(a1+d)^2-(a1+2d)(a1+d)+(a1+3d)=0
a1^2+2da1+d^2-a1^2-3da1-2d^2+a1+3d=0
-da1-d^2+a1+3d=0
(d-1)a1=3d-d^2
(d-1)a1=(2d-1)a1-d^2
da1=d^2
a1=d
x^2-3dx+4d=0
d^2-3d^2+4d=0
-d^2+4d=0
d=0或2
an=nd=2n