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D( x )
x = 0
3*x-15 = 0
x = 0
x = 0
3*x-15 = 0
3*x-15 = 0
3*x-15 = 0 // + 15
3*x = 15 // : 3
x = 15/3
x = 5
x in (-oo:0) U (0:5) U (5:+oo)
(x-5)/(3*x-15) = 2/x // - 2/x
(x-5)/(3*x-15)-(2/x) = 0
(x-5)/(3*x-15)-2*x^-1 = 0
(x-5)/(3*x-15)-2/x = 0
(x*(x-5))/(x*(3*x-15))+(-2*(3*x-15))/(x*(3*x-15)) = 0
x*(x-5)-2*(3*x-15) = 0
x^2-11*x+30 = 0
x^2-11*x+30 = 0
x^2-11*x+30 = 0
DELTA = (-11)^2-(1*4*30)
DELTA = 1
DELTA > 0
x = (1^(1/2)+11)/(1*2) or x = (11-1^(1/2))/(1*2)
x = 6 or x = 5
(x-5)*(x-6) = 0
((x-5)*(x-6))/(x*(3*x-15)) = 0
((x-5)*(x-6))/(x*(3*x-15)) = 0 // * x*(3*x-15)
(x-5)*(x-6) = 0
( x-5 )
x-5 = 0 // + 5
x = 5
( x-6 )
x-6 = 0 // + 6
x = 6
x in { 5}
x = 6
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