Some Special Sequences — Syllabus
NIOS · Class 12 · Mathematics
What Some Special Sequences covers in NIOS Class 12 Mathematics: 4 topics, for the 2026-27 session. Part of the NIOS Class 12 Mathematics syllabus.
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Topics in Some Special Sequences
What is a Series?
- A sequence is an ordered list of numbers following a definite rule, e.g., 1, 4, 9, 16, ...
- A series is formed by adding the terms of a sequence: 1 + 4 + 9 + 16 + ...
- Every sequence has a corresponding series associated with it.
The Three Master Formulas — Σn, Σn², Σn³
- These three formulas are the backbone of this entire chapter. Memorise them perfectly.
- Σn = sum of first n natural numbers = n(n+1)/2
- Σn² = sum of squares of first n natural numbers = n(n+1)(2n+1)/6
Finding Sum of Special Series — Step-by-Step Method
- The METHOD for ALL series sum problems is the same — always follow these 4 steps.
- STEP 1: Find tₙ — identify the nth term of the series by observing the pattern.
- STEP 2: Express tₙ as a polynomial in n — expand any products completely.
Proof of Standard Formulas Using Method of Differences
- The method of differences (telescoping) is used to DERIVE the standard sum formulas.
- For Σn²: Use the identity n³ - (n-1)³ = 3n² - 3n + 1. Write this for n = 1, 2, 3, ..., n and add.
- For Σn³: Use the identity n⁴ - (n-1)⁴ = 4n³ - 6n² + 4n - 1. Write this for n = 1, 2, ..., n and add.
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