## Calculus: Early Transcendentals 8th Edition

$f'(x)=e^{x}(\cos x-\sin x)$
$f(x)=e^{x}\cos x$ Differentiate using the product rule: $f'(x)=(e^{x})(\cos x)'+(\cos x)(e^{x})'=-e^{x}\sin x+e^{x}\cos x=...$ Take out common factor $e^{x}$ to obtain a better looking answer (Optional) $...=e^{x}(\cos x-\sin x)$