Question

ПОМОГИТЕ ПО АЛГЕБРЕ)Прошу вас котики

Answer 1

d = a2-a1

d= -0,4 + 9 = 8,6

an = a1 + d(n-1)

a3 = a1 + 8,6*(3-1)

a3 = -9 + 8,6*2

a3 = 17,2 - 9 = 8,2

a4 = 8,2 +8,6 = 16,8

S4 = -9-0,4+8,2+16,8

S4 = 15,6

Answer 2

Ответ:

$a_3 = 8.6 \\ a_4 = 8.2 \\ S_4 = 15 .6$

Объяснение:

$d = - 0.4 - ( - 9) = - 0.4 + 9 = 8.6$

$a_3 = a_2 + d = - 0.4 + 8.6 = 8.2$

$a_4 = a_3 + d = 8.2 + 8.6 = 16.8$

$S_4 = \frac{2a_1 + d(n - 1)}{2} \times n = \frac{2 \times (- 9) + 8.6 \times 3}{2} \times 4 = \frac{ - 18 + 25.8}{2} \times 4 = \frac{7.8}{2} \times 4 = 7.8 \times 2 = 15.6$