I get the wrong answer for the Derivative of Sin[x]

Questions
,
1

I used

f[x_] = (x^3 + 2 x^2 + 15 x + x)*Sin[ Pi* x];         
Derivative [1][f]

gave a wrong answer. The Derivative of Sin x is Cos x NOT zero. What is wrong?

2

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3

I think you used for the derivation this expression:

D[f, x]

But the right expression must be like this:

D[f[x], x]