Convergence of a GP

Rarely Tested

Convergence of a GP

## Formula

For:

$$a_n=ar^{n-1}$$

if:

$$|r|<1$$

then:

$$\lim_{n\to\infty}a_n=0$$

If:

$$|r|>1$$

the sequence generally does not converge to a finite value unless:

$$a=0$$

## Usage

- Used in limits and infinite-series problems involving geometric progressions.

Question 1

Let $$a_{1}=1$$ and for $$n\geq1,a_{n+1}=\frac{1}{2}a_{n}+\frac{n^{2}-2n-1}{n^{2}(n+1)^2}$$. Then $$\left|\sum_{ n=1}^{ \infty}\left( a_n - \frac{2}{n^2}\right)\right|$$ is equal to ______.

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