2,-1,-4,-7,-10,-13,(-16,)-19
d(разница)=a2-a1=-3
a2=a1+ d = 2+(-3)=-1
a3=a1+2d= 2+(-3*2)=-4
a4=a1+3d=2+(-3*3)=-7
...
a7=a1+6d=2+(-3*6)=-16
2,-1,-4,-7,-10,-13,(-16,)-19
d(разница)=a2-a1=-3
a2=a1+ d = 2+(-3)=-1
a3=a1+2d= 2+(-3*2)=-4
a4=a1+3d=2+(-3*3)=-7
...
a7=a1+6d=2+(-3*6)=-16