Question

а12=-28, а45=-127. найти а1 и d​

Answer 1

а₁₂ = а₁+11d = -28; a₁ = -28-11d

а₄₅ = а₁+44d = -127; a₁ = -127-44d

-28-11d = -127-44d

-11d+44d = -127+28

33d = -99

d = -3.

а₁+11*(-3) = -28

а₁-33 = -28

а₁ = 5