Question

Свойства арифметической прогресси

Answer 1

a₁ = 15            a₂ = 19
a₂ = a₁ + d
d = a₂ - a₁ = 19 - 15 = 4
a₉ = a₁ + 8d = 15 + 8 * 4 = 15 + 32 = 47
a₄₀ = a₁ + 39d = 15 + 39 * 4 = 15 + 156 = 171
Ответ: 47 , 171