Friday 30 October 2015

calculus - Series - $sum_{i=1}^infty (frac{5}{12})^i$ - geometric series?



I have to solve - $$\sum_{i=1}^\infty \left(\frac{5}{12}\right)^i$$ - geometric series?



The geometric series sequence I know is - $$\sum_{i=0}^\infty x_i= \frac{1}{1-x}$$




However in my assignment, the series starts from $i=1$.



The solution I have is - $$\sum_{i=1}^\infty \left(\frac{5}{12}\right)^i = \frac{1}{1-\frac{5}{12}}-1$$



Can you explain please why is that the solution?


Answer



HINT:
$$\sum_{i=0}^\infty x_i= \frac{1}{1-x} =x_0 + \sum_{i=1}^\infty x_i$$


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