Question

if the 8 term of an AP is zero then show that 28 th term is double the 18 th term​

Answer 1

Let the first term of an A.P. = a

And common difference = d

Given: 8th term of an A.P. is 0. Therefore,

a(8-1)d=0

a +7d=0

We have to prove that

T18=2T28

Thus,

T18= a+17d

=-7d+17d

=10d

And

T28=a+27d

=-7d+27d

=20d

From equation (2) and (3),

T18=2T28

Hence proved