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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
3*x^2 = 81/x // - 81/x
3*x^2-(81/x) = 0
3*x^2-81*x^-1 = 0
3*x^2-81*x^-1 = 0
(3*x^3-81*x^0)/(x^1) = 0 // * x^2
x^1*(3*x^3-81*x^0) = 0
x^1
3*x^3-81 = 0
{ 1, -1, 3, -3, 9, -9, 27, -27, 81, -81 }
1
x = 1
3*x^3-81 = -78
1
-1
x = -1
3*x^3-81 = -84
-1
3
x = 3
3*x^3-81 = 0
3
x-3
3*x^2+9*x+27
3*x^3-81
x-3
9*x^2-3*x^3
9*x^2-81
27*x-9*x^2
27*x-81
81-27*x
0
3*x^2+9*x+27 = 0
DELTA = 9^2-(3*4*27)
DELTA = -243
DELTA < 0
x in { 3}
x = 3
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