\( \frac{d}{dx} \left[ \ln (e^x + e^{-x}) \right] = ? \)

\( \frac{d}{dx} \left[ \ln (e^x + e^{-x}) \right] = ? \)

• \( \frac{1}{e^x + e^{-x}} \) (Incorrect)
• \( \frac{e^{2x}}{e^x + e^{-x}} \) (Incorrect)
• \( \frac{e^{-x} - e^x}{e^x + e^{-x}} \) (Incorrect)
• \( \frac{e^x - e^{-x}}{e^x + e^{-x}} \) (Correct)