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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
3-(6/x)-4 = 12 // - 12
3-(6/x)-12-4 = 0
3-6*x^-1-12-4 = 0
-6*x^-1 = 13 // : -6
x^-1 = -13/6
-1 < 0
1/(x^1) = -13/6 // * x^1
1 = -13/6*x^1 // : -13/6
-6/13 = x^1
x = -6/13
x = -6/13
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