Question

помогите решить ¡!!!!!!!!!!!!!!

Answer 1

Формула n-ого члена арифметической прогрессии:  $tt a_n=a_1+d(n-1)$

$tt 4.\\ a_1+8(7-1)=-22 Rightarrow a_1+48=-22 Rightarrow a_1=-22-48=-70\\ a_{19}=-70+8cdot18=-70+144=74\\\ 5.\\ a_1+5(28-1)=42 Rightarrow a_1+135=42 Rightarrow a_1=42-135=-93\\ a_{15}=-93+5cdot14=-93+70=-23$

Answer 2

a₇ = - 22       d = 8       a₁₉ = ?

a₇ = a₁ + 6d

a₁ = a₇ - 6d = - 22 - 6 * 8 = - 22 - 48 = - 70

a₁₉ = a₁ + 18d = - 70 + 18 * 8 = - 70 + 144 = 74

a₂₈ =42       d = 5     a₁₅ = ?

a₂₈ = a₁ + 27d

a₁ = a₂₈ - 27d = 42 - 27 * 5 = 42 - 135 = - 93

a₁₅ = a₁ + 14d = - 93 + 14 * 5 = - 93 + 70 = - 23