Derivative of a plot [closed]

I plotted a graph numerically, so I don’t have a definition of the plotted function. Now I want to plot the derivative of this graph. Is there any way to do it in Mathematica? I have the following plot

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1 Answer
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if I understand you correctly you have the plot not the data.
you need to extract the data from the plot and then (as belisarius mentioned) use interpolation.

Example:

p = Plot[Sin[x], {x, 0, 2 \[Pi]}];
data = Cases[p, Line[{x__}] :> x, -1];
d = D[Interpolation[data][x], x];
Plot[d, {x, 1, 2 \[Pi]}]