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Lesson

Sum of First n Terms

The sum of the first n terms of an AP is given by Sₙ = n/2 [2a + (n − 1)d]. This formula allows the quick calculation of long sums without writing the entire sequence. For example, the sum of the first 20 terms of the AP 2, 5, 8,… is found using a = 2 and d = 3.

45min lesson

Objectives3 goals Lesson12 blocks Review7 assets Practice32 items

Learning objectives

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3 goals

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Understand sum of first n terms in the Arithmetic Progression chapter.
Connect the idea with formulas, examples, and exam-style questions.
Use flashcards, notes, MCQs, and LAQs to check readiness.

Lesson

Step-by-step lesson

12 sections

Concept

Meaning of an Arithmetic Progression

A sequence where each term increases or decreases by a fixed number called the common difference. 💡 Exam Tip: Identify a and d first. For nth term questions, use Tn = a + (n − 1)d. For sum questions, write the sum formula before substitution. ⚠️ Common Mistake: Students often use nd instead of (n − 1)d, or confuse the first term a with the nth term. 📌 Trigger: Find a, find d

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12 lesson sections5 cards / 2 notes18 MCQs / 14 written questions

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Notes

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1
Sum of the First n Terms (Sₙ)
2
Recognising Whether a Sequence Is an A.P.

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32 prompts

18 MCQs14 LAQsMixed test

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In this chapter

Arithmetic Progression

Topic 5 of 7

Now on Sum of First n Terms. Next up: Finite and Infinite APs.

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Arithmetic Progression
nth Term Formula
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Sum of First n Terms

What to understand

Step-by-step lesson

Meaning of an Arithmetic Progression

Meaning of an Arithmetic Progression example

Common Difference (d)

Common Difference (d) example

nth Term Formula (Tn)

nth Term Formula (Tn) example