Last updated at Dec. 8, 2016 by Teachoo

Transcript

Example 12 If the sum of the first 14 terms of an AP is 1050 and its first term is 10, find the 20th term. Here, Sum of the first 14 terms of an AP is 1050. So, S14 = 1050 Also, a = 10 & n = 14 We know that Sum = /2[2 +( 1) ] Putting values 1050 = 14/2[2 (10)+(14 1) ] 1050 = 7[20+13 ] 1050/7=20+13 150 = 20 + 13d 13d = 150 20 13d = 130 d = 10 We have to find 20th term We use the formula an = a + (n 1) d Here a = 10 , d = 10 , n = 20 Putting values is formula an = a + (n 1)d a20 = 10 + (20 1) 10 a20 = 10 + (19 ) 10 a20 = 10 + 190 a20 = 200

Chapter 5 Class 10 Arithmetic Progressions

Serial order wise

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Davneet Singh

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 8 years. He provides courses for Maths and Science at Teachoo. You can check his NCERT Solutions from Class 6 to 12.