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D( x )
5*x-15 = 0
x-3 = 0
5*x-15 = 0
5*x-15 = 0
5*x-15 = 0 // + 15
5*x = 15 // : 5
x = 15/5
x = 3
x-3 = 0
x-3 = 0
x-3 = 0 // + 3
x = 3
x in (-oo:3) U (3:+oo)
(x-4)/(5*x-15) = 1/(x-3) // - 1/(x-3)
(x-4)/(5*x-15)-(1/(x-3)) = 0
(x-4)/(5*x-15)-(x-3)^-1 = 0
(x-4)/(5*x-15)-1/(x-3) = 0
((x-4)*(x-3))/((5*x-15)*(x-3))+(-1*(5*x-15))/((5*x-15)*(x-3)) = 0
(x-4)*(x-3)-1*(5*x-15) = 0
x^2-12*x+27 = 0
x^2-12*x+27 = 0
x^2-12*x+27 = 0
DELTA = (-12)^2-(1*4*27)
DELTA = 36
DELTA > 0
x = (36^(1/2)+12)/(1*2) or x = (12-36^(1/2))/(1*2)
x = 9 or x = 3
(x-3)*(x-9) = 0
((x-3)*(x-9))/((5*x-15)*(x-3)) = 0
((x-3)*(x-9))/((5*x-15)*(x-3)) = 0 // * (5*x-15)*(x-3)
(x-3)*(x-9) = 0
( x-3 )
x-3 = 0 // + 3
x = 3
( x-9 )
x-9 = 0 // + 9
x = 9
x in { 3}
x = 9
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