Subscribe to our Youtube Channel - https://www.youtube.com/channel/UCZBx269Tl5Os5NHlSbVX4Kg
Ex 5.3, 9 - Chapter 5 Class 10 Arithmetic Progressions
Last updated at June 29, 2018 by Teachoo
Transcript
Ex 5.3 ,9 If the sum of first 7 terms of an AP is 49 and that of 17 terms is 289, find the sum of first n terms. We know that Sn = ๐/2 (2๐+(๐โ1)๐) From (1) and (2) 7 โ 3d = 17 โ 8d 8d โ 3d = 17 โ 7 5d = 10 d = 10/5 d = 2 Putting value of d in (1) a = 7 โ 3d a = 7 โ 3 ร2 a = 7 โ 6 a = 1 Hence, a = 1 & d = 2 We need to find sum of first n terms We can use formula Sn = ๐/2 (2a + (n โ 1) d) = ๐/2 (2 ร1+(๐โ1)2) = ๐/2(2+2๐โ2) = ๐/2 (0 + 2n) = ๐/2ร2๐ = n2
Chapter 5 Class 10 Arithmetic Progressions
Serial order wise
About the Author
Davneet Singh
Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 9 years. He provides courses for Maths and Science at Teachoo.