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D( x )
x-30 = 0
x-30 = 0
x-30 = 0
x-30 = 0 // + 30
x = 30
x in (-oo:30) U (30:+oo)
0.1 = 1/(x-30) // - 1/(x-30)
0.1-(1/(x-30)) = 0
0.1-(x-30)^-1 = 0
0.1-1/(x-30) = 0
(0.1*(x-30))/(x-30)-1/(x-30) = 0
0.1*(x-30)-1 = 0
0.1*x-4 = 0
(0.1*x-4)/(x-30) = 0
(0.1*x-4)/(x-30) = 0 // * x-30
0.1*x-4 = 0
0.1*x-4 = 0 // + 4
0.1*x = 4 // : 0.1
x = 4/0.1
x = 40
x = 40
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