A challenging infinite sum with limits

Calculus Level 5

Let { a n } \{ a_n \} satisfy the recurrence relation a n + 1 = ( 1 S n ) c 2 + c ( 1 S n ) 2 c 2 + S n ( 2 S n ) , a_{n+1} = (1-S_n) c^2 + c \sqrt{ (1-S_n)^2 c^2 + S_n (2-S_n) } , where a 1 = 2 c 2 a_1 = 2c^2 , S n = k = 1 n a k S_n = \sum \limits_{k=1}^n a_k , and 0 < c < 1. 0<c<1.

Denote X = lim c 0 + 1 c n = 1 a n 2 X = \lim \limits_{c\to 0^+} \dfrac1c \sum \limits_{n=1}^\infty a_n ^2 . Submit your answer as 1 0 10 X \left \lfloor 10^{10} X \right \rfloor .

Notation: \lfloor \cdot \rfloor denotes the floor function .


The answer is 15707963267.

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1 solution

Prince Zarzees
Oct 28, 2020

Solved it using python .
Link for the code
Looking forward to see the actual process

ANSWER: X = π 2 X = \dfracπ2

Inquisitor Math - 7 months, 2 weeks ago

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