Learn all Concepts of Chapter 5 Class 10 (with VIDEOS). Check - Arithmetic Progressions - Class 10


Last updated at Feb. 11, 2021 by Teachoo
Transcript
Example 15 Find the sum of first 24 terms of the list of numbers whose nth term is given by an = 3 + 2n Given an = 3 + 2n Now 1st term = a1 = 3 + 2 (1) a = 3 + 2 a = 5 2nd term = a2 = 3 + 2 (2) = 3 + 4 = 7 3rd term = a3 = 3 + 2 (3) = 3 + 6 = 9 4th term = a4 = 3 + 2 (4) = 3 + 8 = 11 So, the series is 5, 7, 9, 11 ……… Since 7 – 5 = 2 9 – 7 = 2 11 – 9 = 2 So, difference of consecutive terms is same, So, it is an AP We need to find sum of first 24 terms We use the formula Sn = 𝑛/2[2𝑎+(𝑛−1)𝑑] Where n = 24, a = 5 d = 7 – 5 = 2 Putting these values in formula Sum = 𝑛/2[2𝑎+(𝑛−1)𝑑] = 24/2[2×5+(24−1)2] = 12 [10+(23)(2)] = 12 [10+46] = 12 ×56 = 672 Hence, sum of 24th terms = 672
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