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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
3/51 = 5/x // - 5/x
3/51-(5/x) = 0
3/51-5*x^-1 = 0
-5*x^-1 = -1/17 // : -5
x^-1 = 1/85
-1 < 0
1/(x^1) = 1/85 // * x^1
1 = 1/85*x^1 // : 1/85
85 = x^1
x = 85
x = 85
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