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D( X )
X = 0
X = 0
X = 0
X in (-oo:0) U (0:+oo)
28/X = 0.04 // - 0.04
28/X-0.04 = 0
28*X^-1 = 0.04 // : 28
X^-1 = 0.00142857
-1 < 0
1/(X^1) = 0.00142857 // * X^1
1 = 0.00142857*X^1 // : 0.00142857
700.0007 = X^1
X = 700.0007
X = 700.0007
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