A) Разность d = c4 - c3 = 11 - 7 = 4
Первый член c1 = c3 - 2d = 7 - 2*4 = -1
Сумма первых 9 членов
B) S(9) = (2c1 + 8d)*9/2 = (2(-1) + 8*4)*9/2 = (-2 + 16)*9 = 14*9 = 126
(2^6)^x²-3x+20)<(2^-3)^2x²-6x-200
2^6x²-18x+120<2^-6x²+18x+600
6x²-18x+120<-6x²+18x+600
6x²-18x+120+6x²-18x-600<0
12x²-36x-480<0
x²-3x-40<0
x1+x2=3 U x1*x2=-40⇒x1=-5 U x2=8
+ _ +
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-5 8
x∈(-5;8)
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X^2 - 4px + 4p^2 - 40 = 0
(x-2p)^2 = 40
x = sqrt(40) + 2p
x = -sqrt(40) + 2p