If 9 times the 9th term of an AP is equal to 13 times the 13th term, show that its 22nd term is 0.

Given : 9 × (9th term) = 13 × (13th term)


To prove: 22nd term is 0


9 × (a + 8d) = 13 × (a + 12d)


9a + 72d = 13a + 156d


- 4a = 84d


a = - 21d …..Equation 1


Also 22nd term is given by


a + 21d


Using equation 1 we get


- 21d + 21d = 0


Hence proved 22nd term is 0.


1