Помогите,пожалуйчта(2в)

1) а1 + 6d + a1 + 2d = -8 2a1+8d = -8 a1 +7d-a1-4d = -6 3d = -6 d = -2 2a1-16 = -8 2a1 = 8 a1 = 4 2) 6+12+18... -56 14*6 = 84 84+6 = 90 (2+ 78 = 90 и т.д.) 90* 1/2(14) = 90*7 = 630 630-56 = 574 ответ 574 3) d = -1.8-2.2 = -4 a3 = 2.2+ 4 = 6.2 a6 = -1.8 -4 = -5.8 a3+a6 = 0.4