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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
1-(131.91/x) = 0.68 // - 0.68
1-(131.91/x)-0.68 = 0
1-131.91*x^-1-0.68 = 0
-131.91*x^-1 = -0.32 // : -131.91
x^-1 = 0.0024259
-1 < 0
1/(x^1) = 0.0024259 // * x^1
1 = 0.0024259*x^1 // : 0.0024259
412.21814584 = x^1
x = 412.21814584
x = 412.21814584
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