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D( x )
x^2+3*x = 0
x = 0
x+3 = 0
x^2+3*x = 0
x^2+3*x = 0
x^2+3*x = 0
DELTA = 3^2-(0*1*4)
DELTA = 9
DELTA > 0
x = (9^(1/2)-3)/(1*2) or x = (-9^(1/2)-3)/(1*2)
x = 0 or x = -3
x = 0
x = 0
x+3 = 0
x+3 = 0
x+3 = 0 // - 3
x = -3
x in (-oo:-3) U (-3:0) U (0:+oo)
12/(x^2+3*x)+4/(x+3)+7/x = 0
x^2+3*x = 0
x^2+3*x = 0
x*(x+3) = 0
x+3 = 0 // - 3
x = -3
x*(x+3) = 0
12/(x*(x+3))+4/(x+3)+7/x = 0
12/(x*(x+3))+(4*x)/(x*(x+3))+(7*(x+3))/(x*(x+3)) = 0
7*(x+3)+4*x+12 = 0
4*x+7*x+12+21 = 0
11*x+33 = 0
(11*x+33)/(x*(x+3)) = 0
(11*x+33)/(x*(x+3)) = 0 // * x*(x+3)
11*x+33 = 0
11*x+33 = 0 // - 33
11*x = -33 // : 11
x = -33/11
x = -3
x in { -3}
x belongs to the empty set
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