RootWatch[poly_]:= Module[{rts,pts},
rts=x/. Solve[poly==0,x];
pts=Transpose[{Re [rts],Im[rts]}];
Plot[poly,{x,-10,10},AspectRatio -> 1,PlotRange->{{-10,10},{-10,10}},Epilog->{Directive[Red,PointSize[Large]],Point/@ pts}]
]
{Dynamic[NumberForm[c,{4,2}]],Slider[Dynamic[c],{-2,12}],Dynamic[RootWatch[x^2+5x+c]]}