// k \
|| ___ |
|| \ ` |
|| \ -n k ___|
|| ) n k ___ for a = \/ 0 |
k || / b *\/ 0 |
a *|< /__, |
||n = 1 |
|| |
|| -k / k k\ |
||b*a *\a - b / |
||--------------- otherwise |
\\ a - b /
$$a^{k} \left(\begin{cases} \sum_{n=1}^{k} b^{n} \left(0^{\frac{1}{k}}\right)^{- n} & \text{for}\: a = 0^{\frac{1}{k}} \\\frac{a^{- k} b \left(a^{k} - b^{k}\right)}{a - b} & \text{otherwise} \end{cases}\right)$$
a^k*Piecewise((Sum(b^n*(0^(1/k))^(-n), (n, 1, k)), a = 0^(1/k)), (b*a^(-k)*(a^k - b^k)/(a - b), True))