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D( x )
15*x^2+21*x+6 = 0
15*x^2+21*x+6 = 0
15*x^2+21*x+6 = 0
15*x^2+21*x+6 = 0
DELTA = 21^2-(4*6*15)
DELTA = 81
DELTA > 0
x = (81^(1/2)-21)/(2*15) or x = (-81^(1/2)-21)/(2*15)
x = -2/5 or x = -1
x in (-oo:-1) U (-1:-2/5) U (-2/5:+oo)
(3*x+3)/(15*x^2+21*x+6) = 0
15*x^2+21*x+6 = 0
3*(5*x^2+7*x+2) = 0
5*x^2+7*x+2 = 0
DELTA = 7^2-(2*4*5)
DELTA = 9
DELTA > 0
x = (9^(1/2)-7)/(2*5) or x = (-9^(1/2)-7)/(2*5)
x = -2/5 or x = -1
3*(x+1)*(x+2/5) = 0
(3*x+3)/(3*(x+1)*(x+2/5)) = 0
3*x+3 = 0 // - 3
3*x = -3 // : 3
x = -3/3
x = -1
x in { -1}
x belongs to the empty set
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