а(1) = 5
a(n+1) = a(n) +3
a(8) - ?
a(2) = 5 + 3 = 8
a(3) = 5 + 2*3 = 11
a(8) = 5 + 7*3 = 5 + 21 = 26
( 19 - х^3 ) ^ 1/3 = 3 ;
19 - х^3 = 27 ;
Х^3 = - 8 ;
Х = - 2
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9x^2-7x-2=0
D=49-4(9*(-2)=49+72=121
x1 = (7+11)/18=1
x2 = (7-11)/18 = -4/18 = -2/9
Ответ: x1 = 1; x2 = -2/9