

Examples
Example 2 Important
Example 3
Example 4 Important You are here
Example 5
Example 6 Important
Example 7
Example 8 Important
Example 9
Example 10
Example 11
Example 12
Example 13 Important
Example 14 (i)
Example 14 (ii)
Example 15 Important
Example 16 Important Deleted for CBSE Board 2022 Exams
Last updated at Aug. 3, 2021 by Teachoo
Example 4 Which term of the AP : 21, 18, 15, . . . is –81? Also, is any term 0? Give reason for your answer. Given AP 21, 18, 15, …………. We need to find which term is – 81. Thus, an = – 81 & a = 21 & d = 18 – 21 = –3 We find to find n Putting these in formula an = a + (n – 1) d – 81 = 21 + (n – 1) (–3) – 81 = 21 + n (–3) – 1(–3) – 81 = 21 – 3n + 3 – 81 = 24 – 3n 3n = 24 + 81 3n = 105 n = 105/3 n = 35 Therefore, the 35th term of given AP is –81 Now we have to find which term is 0. an = a + (n – 1)d Here an = 0 , a = 21 & d = –3 We find to find n Putting these in formula an = a + (n – 1) d 0 = 21 + (n – 1) (–3) 0 = 21 + n ( – 3) – 1(–3) 0 = 21 – 3n + 3 0 = 24 – 3n 3n = 24 n = 24/3 n = 8 Therefore, the 8th term of given AP is 0,