CBSE · Class 6-12

Class 11 · Mathematics (041)

Unit 8 · Class 11Mathematics (041)

Algebra

Sequences and Series

Arithmetic and geometric progressions, sum to $n$ terms, arithmetic and geometric means.

Formative-only for boards

Special sums $\sum n$, $\sum n^2$, $\sum n^3$

Learn these concepts — they won't appear in the CBSE 2026-27 board paper.

Lessons

3 concepts

1
Arithmetic Progression
$a_n = a + (n-1)d$ ; $S_n = \tfrac{n}{2}[2a + (n-1)d]$ .
2
Geometric Progression
$a_n = a r^{n-1}$ ; $S_n = a \dfrac{1 - r^n}{1 - r}$ for $r \ne 1$ .
3
AM & GM
AM $= \dfrac{a + b}{2}$ ; GM $= \sqrt{ab}$ . For positive reals AM $\ge$ GM with equality iff $a = b$ .

Skills to practise

Skill · medium

Sequences and Series — Practice (coming soon)

Practice bank for this unit is in progress. You can still read the lessons above.