Find the Rate of Change of the Function $$f ( x ) = - x + \cos x$$

Multiple Choice

Find the rate of change of the function $$f ( x ) = - x + \cos x$$ . ​

A) ​ $- \sin x + 1$
B) ​ $\sin x - 1$
C) ​ $- \sin x - 1$
D) ​ $- \sin x - x$
E) ​ $\sin x + 1$