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0 = x-((3/70)*x^3) // - x-((3/70)*x^3)
(3/70)*x^3-x+0 = 0
(3/70)*x^3-x = 0
3/70*x^3-x = 0
x*(3/70*x^2-1) = 0
3/70*x^2 = 1 // : 3/70
x^2 = 70/3
x^2 = 70/3 // ^ 1/2
abs(x) = (70/3)^(1/2)
x = (70/3)^(1/2) or x = -(70/3)^(1/2)
x = 0
x = 0
x in { (70/3)^(1/2), -(70/3)^(1/2), 0 }
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