Check sibling questions

Ex 5.2, 9 - If 3rd and 9th terms of an AP are 4 and -8 - Ex 5.2

Ex 5.2, 9 - Chapter 5 Class 10 Arithmetic Progressions - Part 2
Ex 5.2, 9 - Chapter 5 Class 10 Arithmetic Progressions - Part 3 Ex 5.2, 9 - Chapter 5 Class 10 Arithmetic Progressions - Part 4


Transcript

Ex 5.2, 9 If the 3rd and the 9th terms of an A.P. are 4 and − 8 respectively. Which term of this A.P. is zero. We know that an = a + (n – 1) d Given 3rd term is 4 a3 = a + (3 – 1) d 4 = a + 2d 4 – 2d = a a = 4 – 2d Given 9th term is –8 a9 = a + (9 – 1) d –8 = a + 8d –8 – 8d = a a = –8d – 8 From (1) & (2) 4 – 2d = –8d – 8 –2d + 8d = –8 – 4 6d = –12 d = (−12)/6 d = –2 Putting value of d in (2) a = 4 – 2d = 4 – 2 × (–2) = 4 + 4 = 8 We need to check which term is 0 Lets assume it is nth term of AP So, an = 0, Also, a = 8 & d = – 2 We know that an = a + (n – 1)d Putting values 0 = 8 + (n – 1) × – 2 0 = 8 + n × ( – 2) – 1 × (– 2) 0 = 8 – 2n + 2 0 = 10 – 2n 2n = 10 n = 10/2 n = 5 ∴ 5th term of AP is 0

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Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 12 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.