Question 2 in an arithmetic progression, the 8th term is twice the 3rd term and the 20th term is 110. a) find the common difference. много 40)

a₈ = 2*a₃

a₂₀ = 110

d - ?

a_n = a₁ + (n-1)*d,

a₈ = a₁ + 7d,

a₃ = a₁ + 2d

a₂₀ = a₁ + 19d,

a₁ + 7d = 2*(a₁ + 2d),

a₁ + 7d = 2a₁ + 4d,

7d - 4d = 2a₁ - a₁

a₁ = 3d,

a₁ + 19d = 110,

3d + 19d = 110,

22d = 110,

d = 110/22 = (11*2*5)/22 = 5.

ответ. d=5.