r - How do I get the derivative of the function? -

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how derivative of following function?

g <- expression(x^2) derivg <- d(g, 'x') derivg # 2 * x g1 <- derivg(2) # error: not find function "derivg"

i want find derivative @ x = 2.

derivg call, not function. evaluate @ x = 2, can do

eval(derivg, list(x = 2)) [1] 4

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