CBSE Class 10 Sample Paper for 2026 Boards - Maths Basic
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CBSE Class 10 Sample Paper for 2026 Boards - Maths Basic
Last updated at September 19, 2025 by Teachoo
This question is similar to Chapter 5 Class 10 Arithmetic Progressions - Ex 5.3
Please check the question here
Transcript
Question 31 The sum of first n terms of an AP is 5𝒏2 − 𝒏. Find the nth term of the AP.Given Sn = 5n2 – n Taking n = 1 S1 = 5 × 12 – 1 = 5 – 1 = 4 ∴ Sum of first term of AP is 4 Taking n = 2 in Sn S2 = 5 × 22 – 2 = 5 × 4 – 2 = 18 ∴ Sum of first 2 terms is 18 But sum of first term will be the first term So, First term = a = 4 Finding 2nd term Sum of first 2 terms = 18 First term + Second term = 18 4 + a2 = 18 a2 = 18 – 4 a2 = 14 Hence, Common difference = d = Second term – First term = 14 – 4 = 10 Thus, our AP looks like 4, 14, 24, … We need to find nth term We know that an = a + (n – 1) d = 4 + (n − 1) × 10 = 4 + 10n – 10 = 10n – 6 Note: We could have also done an = Sn – Sn–1
