If 8times of the 8th term of an AP is equal to 13 times of the 13th term, show that 21st term of an AP is zero.

Asked by Shreyas | 13th Jul, 2018, 08:01: AM

Expert Answer:

According to the question,
8t8 = 13t13 
8(a + 7d) = 13(a + 12d)
8a  +56d = 13a + 156d
13a - 8a + 156d - 56d = 0
5a + 100d = 0
a + 20d = 0
t21 = 0

Answered by Sneha shidid | 13th Jul, 2018, 11:00: AM