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D( X )
X = 0
X = 0
X = 0
X in (-oo:0) U (0:+oo)
66/99 = 1/X // - 1/X
66/99-(1/X) = 0
66/99-X^-1 = 0
-1*X^-1 = -2/3 // : -1
X^-1 = 2/3
-1 < 0
1/(X^1) = 2/3 // * X^1
1 = 2/3*X^1 // : 2/3
3/2 = X^1
X = 3/2
X = 3/2
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