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Finding Sums in the Middle
Last updated at June 9, 2026 by Teachoo
Class 9
Chapter 8 - Predicting What Comes Next: Exploring Sequences & Progress
- Definition
- Explicit Rule for a Sequence
- Recursive Rule for a Sequence
- VirahΔnkaβFibonacci sequence
- Exercise Set 8.1
- Arithmetic Progressions
- Visualising an AP
-
Sum of the First n Natural Numbers
- Exercise Set 8.2
- Geometric Progressions
- Fractals as a GP Sequence
- Visualising a GP
- Exercise Set 8.3
- End-of-Chapter Exercises
Transcript
Finding Sums in the Middle How do we find this sum 25 + 26 + 27 + ... + 58 ? For this we write 25 + 26 + 27 + ... + 58 = (1 + 2 + 3 + 4 + β¦. + 58) β (1 + 2 + 3 + 4 + β¦ 24) = π_58βπ_24 = π/π Γ ππ Γ ππβπ/π Γ ππ Γ ππ = 29 Γ 59 β 12 Γ 25 = 1711 β 300 = 1411
