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