Answer
$f^{\prime}(x)= -2 \sin (2x+7)$
Work Step by Step
We have: $f(x)=\cos (2x+7)$
We need to differentiate both sides with respect to $x$.
$f^{\prime}(x)= -\sin (2x+7) \dfrac{d}{dx} (2x+7)\\=-\sin (2x+7) \times (2)$
Therefore, $f^{\prime}(x)= -2 \sin (2x+7)$
