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x in (-oo:+oo)
85.5 = (0.2*x^2)/3 // - (0.2*x^2)/3
85.5-((0.2*x^2)/3) = 0
85.5-0.06666667*x^2 = 0
-0.06666667*x^2 = -85.5 // : -0.06666667
x^2 = 1282.49993588
x^2 = 1282.49993588 // ^ 1/2
abs(x) = 1282.49993588^(1/2)
x = 1282.49993588^(1/2) or x = -1282.49993588^(1/2)
x in { 1282.49993588^(1/2), -1282.49993588^(1/2) }
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