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x in (-oo:+oo)
0.43*x*x^2*((45-(0.87*x^2))/3) = 0
0.43*x*x^2*((45-0.87*x^2)/3) = 0
(0.43*x^3*(45-0.87*x^2))/3 = 0
( 0.43*x^3 )
0.43*x^3 = 0 // : 0.43
x^3 = 0
x = 0
( 45-0.87*x^2 )
-0.87*x^2 = -45 // : -0.87
x^2 = 51.72413793
x^2 = 51.72413793 // ^ 1/2
abs(x) = 51.72413793^(1/2)
x = 51.72413793^(1/2) or x = -51.72413793^(1/2)
x in { 0, 51.72413793^(1/2), -51.72413793^(1/2) }
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