{an}为等差数列,a7-2a4=-1,a3=0,公差为?

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{an}为等差数列,a7-2a4=-1,a3=0,公差为?{an}为等差数列,a7-2a4=-1,a3=0,公差为?{an}为等差数列,a7-2a4=-1,a3=0,公差为?a3=0嘛,可变为a7-a

{an}为等差数列,a7-2a4=-1,a3=0,公差为?
{an}为等差数列,a7-2a4=-1,a3=0,公差为?

{an}为等差数列,a7-2a4=-1,a3=0,公差为?
a3=0嘛,可变为a7-a4-a4+a3=-1
就是(a7-a4)-(a4-a3)=-1
a4与a3相差d,那么a7与a4相差3d
3d-d=2d,那么2d=-1,d=-1/2

a7=a3+4d a4=a3+d 将这两个式子带入
d=-0.5

a7=a3+4d
a4=a3+d
2a4=2a3+2d
a7-2a4=a3+4d-2a3-2d
因为a3=0所以原式=2d=-1
d=-1/2