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?