Let { x n } be a sequence defined such that x k + 1 = x k 2 + x k with x 1 = 2 1 .
Find the greatest integer less than or equals to the expression below.
x 1 + 1 1 + x 2 + 1 1 + … + x 1 0 0 + 1 1
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Yes.. same , Nice Question ! Loved to working on it!
nice one... i too did the same thing..
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S = k = 1 ∑ 1 0 0 x k + 1 1 = k = 1 ∑ 1 0 0 x k ( x k + 1 ) x k ∵ { x k ( x k + 1 ) = x k + 1 x k 2 = x k + 1 − x k S = k = 1 ∑ 1 0 0 x k + 1 x k = k = 1 ∑ 1 0 0 ( x k + 1 ) x k x k 2 S = k = 1 ∑ 1 0 0 ( x k + 1 ) x k x k + 1 − x k = k = 1 ∑ 1 0 0 x k 1 − x k + 1 1 { ∵ T e l e s c o p i c } S = x 1 1 − x 1 0 0 1 = 2 − x 1 0 0 1
Now we don't need to evaluate x 1 0 0 But we know that given sequence is Increasing , Since It's Nature is Parabolic, So it's increses rapidly , and clearly , x 3 > 1 ⇒ x 1 0 0 > > > 1 ⇒ x 1 0 0 1 < < < 1 1 − < S < 2 − ⌊ S ⌋ = 1