# Wolfram|Alpha behaves strangely with multiple substitutions into derivative

Posted 11 months ago
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 Wolfram|Alpha reacts strangely when I try to substitute multiple variables in a derivation to take the kth derivative of f(x).I've tested all of the individual components of my input, using sin(x) for f(x), and all of them work on their own:Multiple substitution: x*k /. {x->2, k->3} results in:as expected, returning 2*3.Substitution for x into the derivative: D[Sin[x], {x,3}] /. {x->0} results in:again, as expected, returning the 3rd derivative of sin(x) at x=0.Substitution for k into the derivative: D[Sin[x], {x,k}] /. {k->3} results in:once again, as expected, returns the kth derivative of sin(x), where k=3.But if I combine these and try to substitute both x AND k in the derivative: D[Sin[x], {x,k}] /. {x->0, k->3} then Wolfram|Alpha gives up and spits out this:which is a useless regurgitation of its interpretation of the input. What gives? Is there any way I can make this actually work properly?