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D( x )
x+4 = 0
x+4 = 0
x+4 = 0
x+4 = 0 // - 4
x = -4
x in (-oo:-4) U (-4:+oo)
(4*x^2+21*x+25)/(x+4) = 0
4*x^2+21*x+25 = 0
4*x^2+21*x+25 = 0
DELTA = 21^2-(4*4*25)
DELTA = 41
DELTA > 0
x = (41^(1/2)-21)/(2*4) or x = (-41^(1/2)-21)/(2*4)
x = (41^(1/2)-21)/8 or x = (-(41^(1/2)+21))/8
(x+(41^(1/2)+21)/8)*(x-((41^(1/2)-21)/8)) = 0
((x+(41^(1/2)+21)/8)*(x-((41^(1/2)-21)/8)))/(x+4) = 0
( x+(41^(1/2)+21)/8 )
x+(41^(1/2)+21)/8 = 0 // - (41^(1/2)+21)/8
x = -((41^(1/2)+21)/8)
( x-((41^(1/2)-21)/8) )
x-((41^(1/2)-21)/8) = 0 // + (41^(1/2)-21)/8
x = (41^(1/2)-21)/8
x in { -((41^(1/2)+21)/8), (41^(1/2)-21)/8 }
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