If then f'(x) is

Given:

Applying product rule,

⇒

= -x cos x + sin x – 0

⇒ f(x) = -x cos x + sinx

⇒ f'(x) = -[{x(-sinx )} + cosx ] + cosx

= x sin x – cos x + cos x

= x sin x

Correct answer is B.