Example 4 : Which term of the AP: 21, 18, 15,. . . is -81? Also, is an

1.	Example 4 : Which term of the AP: 21, 18, 15,. . . is -81? Also, is any term 0? Givereason for your answer
Answer» For given AP 21, 18, 15.... a=21a+d=17d = -3 a(nth term)= a+(n-1)d-81 = a+(n-1)d-81 = 21+[n-1](-3)-81- 21 = - 3n + 3-102 - 3 = - 3nn = 105/3 = 35 a(nth term)= a+(n-1)d0 = a+(n-1)d0 = 21+[n-1](-3)n-1 = -21/-3n-1 = 7n = 8 Therefore 35th term is - 81 and 8th term is 0

Example 4 : Which term of the AP: 21, 18, 15,. . . is -81? Also, is any term 0? Givereason for your answer

Answer»

For given AP 21, 18, 15....

a=21a+d=17d = -3

a(nth term)= a+(n-1)d-81 = a+(n-1)d-81 = 21+[n-1](-3)-81- 21 = - 3n + 3-102 - 3 = - 3nn = 105/3 = 35

a(nth term)= a+(n-1)d0 = a+(n-1)d0 = 21+[n-1](-3)n-1 = -21/-3n-1 = 7n = 8

Therefore 35th term is - 81 and 8th term is 0