Question

Найдите 5-й член арифметической прогрессии - 1;3;7;...

Answer 1

a₁ = - 1

a₂ = 3

a₂ = a₁ + d

d = a₂ - a₁ = 3 - (- 1) = 3 + 1 = 4

a₅ = a₁ + 4d = - 1 + 4 * 4 = - 1 + 16 = 15