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# Find the derivative of the following functions ( it is to be understood that a, b, c, d, p, q, r and s are fixed non-zero constants and m and n are integers ) $(x^2+1) \cos x$

Let $f(x) = (x^2+1) \cos x$
By product rule,
$f'(x) =(x^2+1) \large\frac{d}{dx}$$(\cos x)+ \cos x\large\frac{d}{dx}$$(x^2+1)$
$= (x^2+1)( - \sin x)+\cos x (2x)$
$= -x^2 \sin x - \sin x+2x\cos x$