2 n = 0 ∑ ∞ ⎣ ⎢ ⎢ ⎢ ⎡ 2 ⎣ ⎢ ⎢ ⎢ ⎡ 2 0 1 3 2 ∑ n = 0 ∞ [ 2 [ 2 0 1 3 2 ∑ n = 0 ∞ [ 2 [ 2 0 1 3 . . . ] n ] − 1 ] n ] − 1 ⎦ ⎥ ⎥ ⎥ ⎤ n ⎦ ⎥ ⎥ ⎥ ⎤ − 1
What is the value of the nested summation above?
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Though the answer comes out correct, their is a mistake towards the end of the solution where 2013 should also be raised to the power n:
∑ n = 0 ∞ x n 2 0 1 3 n = x
Since this goes on for infinity, this can be written as:
2 ∑ n = 0 ∞ [ 2 [ 2 0 1 3 x ] n ] − 1 = x
Now let:
2 ∑ n = 0 ∞ [ 2 [ 2 0 1 3 x ] n ] − 1 = S
∑ n = 0 ∞ [ 2 [ 2 0 1 3 x ] n ] − 1 = 2 S
∑ n = 1 ∞ [ 2 [ 2 0 1 3 x ] n ] − 1 = 2 S [ 2 0 1 3 x ] 1 ∴ ∑ n = 0 ∞ [ 2 [ 2 0 1 3 x ] n ] − 1 − ∑ n = 1 ∞ [ 2 [ 2 0 1 3 x ] n ] − 1 = [ 2 [ 2 0 1 3 x ] 0 ] − 1 = 2 1 = 2 S − 2 S [ 2 0 1 3 x ] 1 = 2 x S x − 2 0 1 3 S
Solving for S gives: S = x − 2 0 1 3 x
And since 2 ∑ n = 0 ∞ [ 2 [ 2 0 1 3 x ] n ] − 1 = x , x − 2 0 1 3 x = x
Solving for x gives x = 2 0 1 4 o r 0
Since x > 0 , x = 2 0 1 4
By the way, can anyone tell me what this method is called?
Call it Poonisation.
I just applied the infinite g.p. formula after putting in x in first step.
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Actually, this is deriving infinite g.p, so its the same thing actually.
I solved it in similar way , nut don't know what it is called .
One of my teacher calls it infinite resistance. Since its similar to the way we solve resistors connected up to infinity
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I have written the solution on a paper. Please see the image .