a4=4,a1与d互为相反数,an=________.
问题描述：
a4=4,a1与d互为相反数,an=________.
答
a4=a1+3d,因为a1=-d,所以a4=-d+3d=2d=4,d=2,
所以a1=-2,
An=-2+(n-1)*2=2n-4