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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
1-(9.99/x) = 0.7 // - 0.7
1-(9.99/x)-0.7 = 0
1-9.99*x^-1-0.7 = 0
-9.99*x^-1 = -0.3 // : -9.99
x^-1 = 0.03003003
-1 < 0
1/(x^1) = 0.03003003 // * x^1
1 = 0.03003003*x^1 // : 0.03003003
33.30000003 = x^1
x = 33.30000003
x = 33.30000003
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