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 2 added 335 characters in body edited Feb 11 '13 at 17:42 Dr. belisarius 109k1111 gold badges173173 silver badges391391 bronze badges RegionPlot[ And @@ Thread[(Re[sol /. z -> (a + b I)]) < 0], {a, 3, 10}, {b, -10, 10}]  Edit As per your edit, z is Real (really bad choice for a name), so: Plot[Re[sol], {z, -1, 10}, Evaluated -> True, PlotRange -> {-2, 2}]  You can see that from z==4 onwards, the two complex conjugate solutions are negative, as well as the real one. RegionPlot[ And @@ Thread[(Re[sol /. z -> (a + b I)]) < 0], {a, 3, 10}, {b, -10, 10}]  RegionPlot[ And @@ Thread[(Re[sol /. z -> (a + b I)]) < 0], {a, 3, 10}, {b, -10, 10}]  Edit As per your edit, z is Real (really bad choice for a name), so: Plot[Re[sol], {z, -1, 10}, Evaluated -> True, PlotRange -> {-2, 2}]  You can see that from z==4 onwards, the two complex conjugate solutions are negative, as well as the real one. 1 answered Feb 11 '13 at 14:31 Dr. belisarius 109k1111 gold badges173173 silver badges391391 bronze badges RegionPlot[ And @@ Thread[(Re[sol /. z -> (a + b I)]) < 0], {a, 3, 10}, {b, -10, 10}]