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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
(2/5)*x = 1/x-4 // - 1/x-4
(2/5)*x-(1/x)+4 = 0
(2/5)*x-x^-1+4 = 0
2/5*x^1-1*x^-1+4*x^0 = 0
(2/5*x^2+4*x^1-1*x^0)/(x^1) = 0 // * x^2
x^1*(2/5*x^2+4*x^1-1*x^0) = 0
x^1
(2/5)*x^2+4*x-1 = 0
(2/5)*x^2+4*x-1 = 0
DELTA = 4^2-(-1*4*(2/5))
DELTA = 88/5
DELTA > 0
x = ((88/5)^(1/2)-4)/(2*(2/5)) or x = (-(88/5)^(1/2)-4)/(2*(2/5))
x = 5/4*((88/5)^(1/2)-4) or x = -5/4*((88/5)^(1/2)+4)
x in { -5/4*((88/5)^(1/2)+4), 5/4*((88/5)^(1/2)-4)}
x in { -5/4*((88/5)^(1/2)+4), 5/4*((88/5)^(1/2)-4) }
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