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D( x )
x+3 = 0
3*x+1 = 0
(3*x-x^2)/(3*x+1) = 0
x+3 = 0
x+3 = 0
x+3 = 0 // - 3
x = -3
3*x+1 = 0
3*x+1 = 0
3*x+1 = 0 // - 1
3*x = -1 // : 3
x = -1/3
(3*x-x^2)/(3*x+1) = 0
(3*x-x^2)/(3*x+1) = 0
3*x-x^2 = 0
x*(3-x) = 0
3-x = 0 // - 3
-x = -3 // * -1
x = 3
x*(x-3) = 0
(x*(x-3))/(3*x+1) = 0
( x-3 )
x-3 = 0 // + 3
x = 3
( x )
x = 0
x in (-oo:-3) U (-3:-1/3) U (-1/3:0) U (0:3) U (3:+oo)
((15-(5*x))/(x+3))/((3*x-x^2)/(3*x+1)) = 0
((15-5*x)/(x+3))/((3*x-x^2)/(3*x+1)) = 0
((15-5*x)*(3*x+1))/((x+3)*(3*x-x^2)) = 0
3*x-x^2 = 0
x*(3-x) = 0
3-x = 0 // - 3
-x = -3 // * -1
x = 3
x*(x-3) = 0
((15-5*x)*(3*x+1))/(x*(x+3)*(x-3)) = 0
( 15-5*x )
15-5*x = 0 // - 15
-5*x = -15 // : -5
x = -15/(-5)
x = 3
( 3*x+1 )
3*x+1 = 0 // - 1
3*x = -1 // : 3
x = -1/3
x in { 3}
x in { -1/3}
x belongs to the empty set
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