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D( X )
X = 0
X = 0
X = 0
X in (-oo:0) U (0:+oo)
3.5/X = 2.5/405 // - 2.5/405
3.5/X-(2.5/405) = 0
3.5/X-0.00617284 = 0
3.5*X^-1 = 0.00617284 // : 3.5
X^-1 = 0.00176367
-1 < 0
1/(X^1) = 0.00176367 // * X^1
1 = 0.00176367*X^1 // : 0.00176367
566.99949537 = X^1
X = 566.99949537
X = 566.99949537
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