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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
0 = 9*x-(81/x)-9 // - 9*x-(81/x)-9
81/x-(9*x)+0+9 = 0
81/x-9*x+0+9 = 0
81*x^-1-9*x^1+9*x^0 = 0
(9*x^1-9*x^2+81*x^0)/(x^1) = 0 // * x^2
x^1*(9*x^1-9*x^2+81*x^0) = 0
x^1
9*x-9*x^2+81 = 0
9*x-9*x^2+81 = 0
DELTA = 9^2-(-9*4*81)
DELTA = 2997
DELTA > 0
x = (2997^(1/2)-9)/(-9*2) or x = (-2997^(1/2)-9)/(-9*2)
x = (9*37^(1/2)-9)/(-18) or x = (-9*37^(1/2)-9)/(-18)
x in { (9*37^(1/2)-9)/(-18), (-9*37^(1/2)-9)/(-18)}
x in { (9*37^(1/2)-9)/(-18), (-9*37^(1/2)-9)/(-18) }
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