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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
1.3/1.2 = 6.5/x // - 6.5/x
1.3/1.2-(6.5/x) = 0
1.3/1.2-6.5*x^-1 = 0
-6.5*x^-1 = -1.08333333 // : -6.5
x^-1 = 0.16666667
-1 < 0
1/(x^1) = 0.16666667 // * x^1
1 = 0.16666667*x^1 // : 0.16666667
5.99999988 = x^1
x = 5.99999988
x = 5.99999988
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