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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
0.839 = 8/x // - 8/x
0.839-(8/x) = 0
0.839-8*x^-1 = 0
-8*x^-1 = -0.839 // : -8
x^-1 = 0.104875
-1 < 0
1/(x^1) = 0.104875 // * x^1
1 = 0.104875*x^1 // : 0.104875
9.53516091 = x^1
x = 9.53516091
x = 9.53516091
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