1.Найдите 18-ый член арифметической прогрессии (Сn), если: а)c1=-7.2; d=0.6; б)c1=5.6;с2=4,82.Найдите разность

1. с_n = c₁ + d * (n 1).

a) c₁ = -7.2; d = 0.6;

с₁₈ = -7.2 + 0.6 * (18 1) = -7.2 + 0.6 * 17 = -7.2 + 10.2 = 3.

б) c₁ = 5,6; c₂ = 4.8;

d = 4.8 5.6 = -0.8;

с₁₈ = 5.6 - 0.8 * (18 1) = 5.6 0.8 * 17 = 5.6 13.6 = -8.

Ответ. а) 3. б) -8.

2. k₁ = 6.2; k₁₀ - 2k₃ = -11.85;

k₁₀ = 6.2 + 9d;

k₃ = 6.2 + 2d;

6.2 + 9d 2 * (6.2 + 2d) = -11.85;

5d 6.2 = -11.85;

5d = -11.85 + 6.2;

5d = -5.65;

d = -1.13.

Ответ. -1,13.

3. a₁ = 18, a₆ = -3.6;

a₆ = a₁ + 5d;

-3.6 = 18 + 5d;

5d = -21.6;

d = -4.32;

a₂ = 18 4.32 = 13.68;

a₃ = 13.68 4.32 = 9.36;

a₄ = 9.36 4.32 = 5.04;

a₅ = 5.04 4.32 = 0.72;

a₆ = 0.72 4.32 = -3.6.

Ответ. 13,68; 9,36; 5,04; 0,72.