For given positive values $\displaystyle a_{1},\ldots,a_{n}$, I have the power mean: $\displaystyle P(\alpha):=\left(\frac{1}{n}\sum_{k=1}^{n}a_{k}^{\ alpha}\right)^{\frac{1}{\alpha}}$ for which I need to find $\displaystyle \frac{d}{d\alpha}P(\alpha)$. Please Help!!!