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Tuesday, December 29, 2015

2015/116) Find the limit of the product as k goes to infinite \prod_{n=1}^{k}\frac{n^2}{n^2-1}

We propose \prod_{n=1}^{k}\frac{n^2}{n^2-1}=\frac{2k}{k+1}

for n =2 we have product = \frac{4}{3} = \frac{2 * 2}{2+1}

let it be true of n = k

so we have \prod_{n=1}^{k}\frac{n^2}{n^2-1}=\frac{2k}{k+1}

multiply by (k+1)st term to get   f(k+1) = \prod_{n=1}^{k}\frac{n^2}{n^2-1} * \frac{(k+1)^2}{(k+1)^2 - 1}
= \frac{2k}{k+1} * \frac{(k+1)^2}{k(k+2)} = \frac{2 * (k +1)}{(k+2)}
so if it is true for k it is true for k + 1
Now that we have found the closed form as k goes to infinite above product goes to 2 (converges to 2)

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