f(x)=x^pi
Thanks
For arbitrary $\displaystyle b\in\mathbb{R}$, $\displaystyle x^b$ is defined to be nothing other than the value of $\displaystyle \mathrm{e}^{b\cdot\ln(x)}$. If you can define $\displaystyle \ln(x)$ for negative x, fine (I would be surprised if you could, but then: who am I?), if you can't: there you go!