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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
5/3-(4*x) = 40/x-(6*x) // - 40/x-(6*x)
6*x-(4*x)-(40/x)+5/3 = 0
6*x-4*x-40*x^-1+5/3 = 0
2*x^1-40*x^-1+5/3*x^0 = 0
(2*x^2+5/3*x^1-40*x^0)/(x^1) = 0 // * x^2
x^1*(2*x^2+5/3*x^1-40*x^0) = 0
x^1
2*x^2+(5/3)*x-40 = 0
2*x^2+(5/3)*x-40 = 0
DELTA = (5/3)^2-(-40*2*4)
DELTA = 2905/9
DELTA > 0
x = ((2905/9)^(1/2)-(5/3))/(2*2) or x = (-(5/3)-(2905/9)^(1/2))/(2*2)
x = ((2905/9)^(1/2)-5/3)/4 or x = (-((2905/9)^(1/2)+5/3))/4
x in { (-((2905/9)^(1/2)+5/3))/4, ((2905/9)^(1/2)-5/3)/4}
x in { (-((2905/9)^(1/2)+5/3))/4, ((2905/9)^(1/2)-5/3)/4 }
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