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D( x )
x+4 = 0
x = 0
x+4 = 0
x+4 = 0
x+4 = 0 // - 4
x = -4
x = 0
x = 0
x in (-oo:-4) U (-4:0) U (0:+oo)
9/x = x/(x+4) // - x/(x+4)
9/x-(x/(x+4)) = 0
(-1*x)/(x+4)+9/x = 0
(-1*x^2)/(x*(x+4))+(9*(x+4))/(x*(x+4)) = 0
9*(x+4)-1*x^2 = 0
9*x-x^2+36 = 0
9*x-x^2+36 = 0
9*x-x^2+36 = 0
DELTA = 9^2-(-1*4*36)
DELTA = 225
DELTA > 0
x = (225^(1/2)-9)/(-1*2) or x = (-225^(1/2)-9)/(-1*2)
x = -3 or x = 12
(x+3)*(x-12) = 0
((x+3)*(x-12))/(x*(x+4)) = 0
((x+3)*(x-12))/(x*(x+4)) = 0 // * x*(x+4)
(x+3)*(x-12) = 0
( x+3 )
x+3 = 0 // - 3
x = -3
( x-12 )
x-12 = 0 // + 12
x = 12
x in { -3, 12 }
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