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D( r )
2*r+4 = 0
3*r+6 = 0
2*r+4 = 0
2*r+4 = 0
2*r+4 = 0 // - 4
2*r = -4 // : 2
r = -4/2
r = -2
3*r+6 = 0
3*r+6 = 0
3*r+6 = 0 // - 6
3*r = -6 // : 3
r = -6/3
r = -2
r in (-oo:-2) U (-2:+oo)
1/(2*r+4)+4/(3*r+6) = 0
(1*(3*r+6))/((2*r+4)*(3*r+6))+(4*(2*r+4))/((2*r+4)*(3*r+6)) = 0
1*(3*r+6)+4*(2*r+4) = 0
11*r+22 = 0
(11*r+22)/((2*r+4)*(3*r+6)) = 0
(11*r+22)/((2*r+4)*(3*r+6)) = 0 // * (2*r+4)*(3*r+6)
11*r+22 = 0
11*r+22 = 0 // - 22
11*r = -22 // : 11
r = -22/11
r = -2
r in { -2}
r belongs to the empty set
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