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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
x-(4/x) = 15/x+4 // - 15/x+4
x-(4/x)-(15/x)-4 = 0
x-4*x^-1-15*x^-1-4 = 0
1*x^1-19*x^-1-4*x^0 = 0
(1*x^2-4*x^1-19*x^0)/(x^1) = 0 // * x^2
x^1*(1*x^2-4*x^1-19*x^0) = 0
x^1
x^2-4*x-19 = 0
x^2-4*x-19 = 0
DELTA = (-4)^2-(-19*1*4)
DELTA = 92
DELTA > 0
x = (92^(1/2)+4)/(1*2) or x = (4-92^(1/2))/(1*2)
x = (2*23^(1/2)+4)/2 or x = (4-2*23^(1/2))/2
x in { (4-2*23^(1/2))/2, (2*23^(1/2)+4)/2}
x in { (4-2*23^(1/2))/2, (2*23^(1/2)+4)/2 }
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