If an antiderivative of $f\left( x \right)$ is ${ e }^{ x }$ and that of $g\left( x \right)$ is $\cos { x }$, then $\displaystyle \int { f\left( x \right) \cos { x } \ dx } +\int { g\left( x \right) { e }^{ x } \ dx }$ is equal to

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