How to find a limit to $\sum_{r=2}^{\infty}\frac{1}{2^{r-1}}$?

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I know that the limit is one, but what are the steps to take in order to find a limit? Maybe there are sources online where it is explained in detail?

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hint

As a geometric series,

$$S=\frac 12+\frac 14+\frac 18+....$$ $$=\frac 12(1+S)$$

$$\implies 2S=1+S$$