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D( x )
x^2 = 0
x^2 = 0
x^2 = 0
1*x^2 = 0 // : 1
x^2 = 0
x = 0
x in (-oo:0) U (0:+oo)
-1/(x^2) = -1/3 // + -1/3
-1/(x^2)-(-1/3) = 0
1/3-1/(x^2) = 0
-1*x^-2 = -1/3 // : -1
x^-2 = 1/3
-2 < 0
1/(x^2) = 1/3 // * x^2
1 = 1/3*x^2 // : 1/3
3 = x^2
x^2 = 3 // ^ 1/2
abs(x) = 3^(1/2)
x = 3^(1/2) or x = -3^(1/2)
x in { 3^(1/2), -3^(1/2) }
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