Summation of powers inequality Can anyone provide a slick proof of the following?
Let $0 < x \le 1$.  Then $\displaystyle \sum_{k=0}^{n-1} x^k \ge \frac {1} {1 - (1 - 1/n)x}$.

As $1-(1-1/n)x>0$, we have to show that $(1-x)\sum_{k=0}^{n-1}x^k+\frac 1n\sum_{k=0}^{n-1}x^{k+1}\geq 1$. This is equivalent to 
$$1-x^n+\frac 1n\sum_{j=1}^nx^j\geq 1,$$
i.e.,
$$nx^n\leq \sum_{j=1}^nx^j.$$
This is true, as each terms in the sum is $\geq x^n$.
