Difference between revisions of "AoPS Wiki talk:Problem of the Day/August 1, 2011"
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{{:AoPSWiki:Problem of the Day/August 1, 2011}} | {{:AoPSWiki:Problem of the Day/August 1, 2011}} | ||
==Solution== | ==Solution== | ||
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We can split this summation, as shown: | We can split this summation, as shown: | ||
<math> \sum_{k = 1}^{\infty}{\frac{8+2^{k}}{4^{k}}} = \sum_{k = 1}^{\infty}{\frac{8}{4^{k}}} +\sum_{k = 1}^{\infty}{\frac{2^k}{4^{k}}} </math>. | <math> \sum_{k = 1}^{\infty}{\frac{8+2^{k}}{4^{k}}} = \sum_{k = 1}^{\infty}{\frac{8}{4^{k}}} +\sum_{k = 1}^{\infty}{\frac{2^k}{4^{k}}} </math>. |
Latest revision as of 14:20, 1 August 2011
Problem
AoPSWiki:Problem of the Day/August 1, 2011
Solution
We can split this summation, as shown:
.
Now we must simply find each of the smaller sums, and add them.
:
We can use the formula for the sum of an infinite geometric series ( where
is the first term and
is the common ratio).
and
since each term is getting multiplied by
to receive the next term. Therefore, this sum is:
.
:
Similarly, we can use the formula used to solve the first part.
and
. Therefore, this sum is:
.
Using these two answers, the desired sum is: .