In[]:=
Manipulate[ Show[{Plot[1/(4 p) x^2, {x, -10, 10}, PlotRange  {{-10, 10}, {-1, 10}}], Graphics[{Red, PointSize[.015], Point[{0, p}]}, PlotRange  {{-10, 10}, {-1, 10}}]}], {p, .01, 10, .1}]
Out[]=
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p
-10
-5
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10
2
4
6
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10
In[]:=
Manipulate[ Show[{Plot[1/(4 p) x^2, {x, -10, 10}, PlotRange  {{-10, 10}, {-1, 10}}], Graphics[{Red, PointSize[.015], Point[{0, p}], Tooltip[Point[{0, p}], {0, p}]}, PlotRange  {{-10, 10}, {-1, 10}}]}], {p, .01, 10, .1}]
Out[]=
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p