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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
x+8/x = -9 // + 9
x+8/x+9 = 0
1*x^1+8*x^-1+9*x^0 = 0
(1*x^2+9*x^1+8*x^0)/(x^1) = 0 // * x^2
x^1*(1*x^2+9*x^1+8*x^0) = 0
x^1
x^2+9*x+8 = 0
x^2+9*x+8 = 0
DELTA = 9^2-(1*4*8)
DELTA = 49
DELTA > 0
x = (49^(1/2)-9)/(1*2) or x = (-49^(1/2)-9)/(1*2)
x = -1 or x = -8
x in { -8, -1}
x in { -8, -1 }
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