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easy geometric series

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Theorem.

n - 1
-----  i    n
)     2  = 2  - 1
-----
i = 0

Proof.

Clearly, this is a geometric series, but one can also use the power of induction. For n=1, the statement is trivially states

 0    1
2  = 2  - 1

Let’s suppose our theorem holds for every number below n>1. What about n itself?

  n             n - 1           /        \
-----  i    n   -----  i    n   |  n     |    n + 1
)     2  = 2  + )     2  = 2  + | 2  - 1 | = 2      - 1
-----           -----           \        /
i = 0           i = 0

QuED…

Written by grault

January 26, 2008 - 11:01 pm at January 26, 2008 - 11:01 pm

Posted in math

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