Sigma Percentile
JEE Main 2022 (29 July Shift 1)
LEVELJEE Main

Animated Solution for Mathematics - Sequence and Series: If , then is equal to ________.

Enter Numerical Value:

Visualized Solution

Pattern Recognition

  • Given Series:
  • Target: Find where the sum equals .

Defining the General Term

  • General term:
  • Summation limits: to

The Method of Differences

  • Goal: Express as the difference of two consecutive terms .
  • Consider the difference of outer factors: .

Adjusting the Numerator

  • Multiply and divide by .
  • Rewrite :

Splitting the Fraction

  • Split into two parts:
  • Simplified form:

The Summation Setup

  • Total Sum

Expanding the First Few Terms

  • For :
  • For :
  • For :

The Last Term and Telescoping

  • For :
  • Telescoping cancellation leaves only the first and last parts.

Finding a Common Denominator

  • Note:

Simplifying the Numerator

  • Numerator becomes

Further Simplification

  • Divide numerator and denominator by :

Comparing with the Given Form

  • Given:
  • From our calculation:
  • Therefore,

Final Calculation

  • Calculate :
  • Final Answer:

The Sigma Insight: Sum of Special Series

Analyzing the Setup

The given series is:
This is a classic telescoping series. The general term for this series, where ranges from to , is defined as:

The Method of Differences

To solve this, we employ the Method of Differences (or the method). We aim to express as the difference of two consecutive terms, .
Observe the outer factors of the denominator: and . Their difference is .
We multiply and divide the expression by to introduce this difference into the numerator:

The Domino Effect

Splitting this into two separate fractions reveals the telescoping structure:
Simplifying the expression, we obtain:
As we sum these terms from to , the intermediate terms cancel out. We are left only with the first positive fraction and the last negative fraction:

The Final Calculation

We simplify the sum :
Since , we find a common denominator:
Dividing the numerator and denominator by , we get:
Given the form , we identify . Therefore, the final value is:

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