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D( X )
X = 0
X = 0
X = 0
X in (-oo:0) U (0:+oo)
41.19/X = 80 // - 80
41.19/X-80 = 0
41.19*X^-1 = 80 // : 41.19
X^-1 = 1.94221899
-1 < 0
1/(X^1) = 1.94221899 // * X^1
1 = 1.94221899*X^1 // : 1.94221899
0.514875 = X^1
X = 0.514875
X = 0.514875
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