Class 11 Maths Chapter 8 Sequences and Series – Revision Notes

Quick revision notes for Class 11 Maths Chapter 8 (Sequences and Series). These Class 11 Maths Chapter 8 notes are ideal for quick revision just before exams.

AP (Recap)

• a_n=a+(n−1)d; S_n=n/2[2a+(n−1)d].

GP

• Common ratio r; a_n=arⁿ⁻¹.
• S_n=a(rⁿ−1)/(r−1), r≠1.
• Infinite GP (|r|<1): S∞=a/(1−r).

Means

• AM=(a+b)/2; GM=√(ab); AM≥GM (positive numbers).

Special Series

• ∑n = n(n+1)/2.
• ∑n² = n(n+1)(2n+1)/6.
• ∑n³ = [n(n+1)/2]².

One-Line Summary

Sequences follow AP (constant difference) or GP (constant ratio) patterns, with distinct nth-term and sum formulas, and an infinite GP converges to a finite sum only when |r|<1.

Written by Satish

NCERTBooks.org is an independent educational resource run by a small team focused on making official NCERT textbooks easy to find, read, and download for students, parents, and teachers across India. We are not affiliated with NCERT or the Ministry of Education -- we organise publicly available NCERT content by class and subject, verify links against official sources, and build tools (like our in-browser reader) that make studying more convenient. Every guide we publish is written and reviewed by our team based on the actual NCERT curriculum and syllabus.