\(\lim _{\mathrm{n} \rightarrow \infty}\left[\left(1 / \mathrm{n}^{2}\right)+\left(2 / \mathrm{n}^{2}\right)+\left(3 / \mathrm{n}^{2}\right)+\ldots \ldots\left\\{(\mathrm{n}-1) / \mathrm{n}^{2}\right\\}\right]=?\) (a) \((1 / 2)\) (b) 2 (c) (d) \((2 / 3)\)

Short Answer

Expert verified
The short answer is (a) \(\frac{1}{2}\).

Step by step solution

01

Express the sum in Sigma notation

We can express the given sum using the Sigma notation, an indexed summation for a sequence of terms. Note that the terms are of the form \(\frac{k}{n^2}\) where k goes from 1 to (n-1). So, we can write: \[\sum_{k=1}^{n-1} \frac{k}{n^2}\]
02

Factor out n^2

Now, let's factor out the common denominator \(n^2\) from the sum: \[\frac{1}{n^2} \sum_{k=1}^{n-1} k\]
03

Solve the sum (Sum of first n-1 natural numbers)

The sum of the first (n-1) natural numbers has the formula: \[\sum_{k=1}^{n-1} k = \frac{(n-1)(n-2)}{2}\] So, the given expression becomes: \[\frac{1}{n^2} \cdot \frac{(n-1)(n-2)}{2}\]
04

Simplify and find the limit

Now, simplify the expression and find the limit as n approaches infinity: \[\lim_{n \to \infty} \frac{1}{n^2} \cdot \frac{(n-1)(n-2)}{2} = \lim_{n \to \infty} \frac{(n-1)(n-2)}{2 n^{2}}\] Divide numerator and denominator by \(n^2\), it becomes: \[\lim_{n \to \infty} \frac{1 - \frac{1}{n} - \frac{2}{n^2}}{2}\] Now, apply the limit: \[\lim_{n \to \infty} \frac{1 - \frac{1}{n} - \frac{2}{n^2}}{2} = \frac{1 - 0 - 0}{2}\]
05

Final answer

Evaluate the final expression: \[\frac{1}{2}\] So, the answer is (a) \(\frac{1}{2}\).

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