Will it converge?

Calculus Level 5

Let a series be defined, for some real value of a 0 a_0 and α ( > 0 ) \alpha(>0) as:

a n = a n 1 + α sin ( a n 1 ) \displaystyle \large a_n=a_{n-1}+\alpha \sin(a_{n-1})

X = lim n a n X=\lim _{ n\rightarrow \infty }{ { a }_{ n } }

Let S S be the sum of all the distinct values of X X as a 0 a_0 varies from [ 1 , 100 ] [1,100] and α \alpha varies over all positive reals.

Find 1 0 4 S \left\lfloor 10^4S \right\rfloor

Details and Assumptions:

  1. X X must be finite.

  2. α \alpha is a variable independent of a 0 a_0 and can take any positive value.

This is part of my set Powers of the ordinary .


The answer is 15582299.

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1 solution

But in the note, the solution you've provided has a line

provided the value of α \alpha is not too large.

which is not there in this question.

Siddhartha Srivastava - 6 years, 3 months ago

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Oh, I'm sorry, my phrasing of the question seems to have got across the wrong message. In this question, α \alpha is intended as a variable. The aim is to find all X X for different values of α \alpha and a 0 a_0 . I have edited the question. Thanks for your suggestion @Siddhartha Srivastava

Raghav Vaidyanathan - 6 years, 3 months ago

don't you think it will be better if you had simply asked s \left\lfloor s \right\rfloor ! :)

Deepanshu Gupta - 6 years, 3 months ago

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Yes, in hindsight, that seems to be a better choice. But it's okay, no harm done.

Raghav Vaidyanathan - 6 years, 3 months ago

Can you please give an example of a sequence that converges to 32 π 32\pi

Cause I can't find one. Please help @Raghav Vaidyanathan

Ronak Agarwal - 6 years, 3 months ago

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@Ronak Agarwal For 32 π 32\pi , just put a 0 = 32 π a_{0}=32\pi . But in the question we need a 0 100 a_0\le 100 hence we only consider till 31 π 31\pi

Raghav Vaidyanathan - 6 years, 3 months ago

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