You are here
Question 7 - Finding sum from nth number - Chapter 8 Class 11 Sequences and Series
Last updated at July 28, 2026 by Teachoo
Chapter 8 Class 11 Sequences and Series
Concept wise
- Finding Sequences
- Arithmetic Progression (AP): Formulae based
- Arithmetic Progression (AP): Statement
- Arithmetic Progression (AP): Calculation based/Proofs
- Inserting AP between two numbers
- Arithmetic Mean (AM)
- Geometric Progression(GP): Formulae based
- Geometric Progression(GP): Statement
- Geometric Progression(GP): Calculation based/Proofs
- Inserting GP between two numbers
- Geometric Mean (GM)
- AM and GM (Arithmetic Mean And Geometric mean)
- AP and GP mix questions
- Finding sum from series
-
Finding sum from nth number
Transcript
Question 7, Find the sum to n terms of the series whose nth term is n (n+3). Given an = n (n + 3) = n2 + 3n The sum of n terms is = (n( n + 1)(2n + 1))/6 + (3n( n + 1) )/2 = (n(n + 1))/2 (( (2n + 1))/3 " + 3" ) = (n(n + 1))/2 (( (2n + 1) + 9)/3) = (n(n+1))/2 × (( 2𝑛 +10 )/3) = (n(n+1))/2 × ( 2(𝑛 +5) )/3 = (n( n + 1)(n + 5) )/3 Thus, the required sum is (n( n + 1)(n + 5) )/3
