\text { 15. Find the derivative of } f(x)=\ln (\sqrt{3 x}) \text {. } \text { A) } f^{\prime}(x)=\frac{1}{6 x} \text { B) } f^{\prime}(x)=\frac{2}{3 x} \text { C) } f^{\prime}(x)=\frac{1}{2 x} f^{\prime}(x)=\frac{1}{2}\left[\frac{1}{x}+\frac{1}{3}\right]

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