A2=18, a3=14, S8=?, d=?, an=?

D=A₃ - A₂

d=14-18 = - 4

A₂=A₁+d

18=A₁ - 4

A₁=22

A₈=A₁+7d

A₈ = 22 + 7 * (-4) = 22 - 28 = - 6

S₈ = (A₁+A₈) * 8 = 4 (22 - 6) = 4*16=64

2

An=A₁+d (n-1)

An=22-4 (n-1) = 22-4n+4=26-4n

Ответ: S₈ = 64;

An=26-4n