Covariant derivative of a function

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I want to determine the covariant derivativeJe veut déterminer la derivée covariante [tex]▽_{X}(e^{-f})[/tex], where X is a vector field over a manifold and f is a [tex]C^{∞}[/tex] function
Is it: [tex]▽_{X}(e^{-f})=e^{-f}<▽f,X>[/tex], or another similar relation?