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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
(2/5)*x = 1/x-3/15 // - 1/x-3/15
(2/5)*x-(1/x)-(-3/15) = 0
(2/5)*x-x^-1+1/5 = 0
2/5*x^1-1*x^-1+1/5*x^0 = 0
(2/5*x^2+1/5*x^1-1*x^0)/(x^1) = 0 // * x^2
x^1*(2/5*x^2+1/5*x^1-1*x^0) = 0
x^1
(2/5)*x^2+(1/5)*x-1 = 0
(2/5)*x^2+(1/5)*x-1 = 0
DELTA = (1/5)^2-(-1*4*(2/5))
DELTA = 41/25
DELTA > 0
x = ((41/25)^(1/2)-(1/5))/(2*(2/5)) or x = (-(1/5)-(41/25)^(1/2))/(2*(2/5))
x = 5/4*((41/25)^(1/2)-1/5) or x = -5/4*((41/25)^(1/2)+1/5)
x in { -5/4*((41/25)^(1/2)+1/5), 5/4*((41/25)^(1/2)-1/5)}
x in { -5/4*((41/25)^(1/2)+1/5), 5/4*((41/25)^(1/2)-1/5) }
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