Given: 7th term is 34 and 8th term is 64

To find: find its 18th term

34 = a + 6d ………….equation1

64 = a + 12d ………… equation2

Subtract equation1 from equation2 we get

d = 5

Put in equation1 we get

a = 4

So 18th term is

4 + 17 × 5 = 89

If 7th and 13th terms of an AP be 34 and 64 respectively then find its 18thterm.

If 7th and 13th terms of an AP be 34 and 64 respectively then find its 18thterm.

Given: 7th term is 34 and 8th term is 64

To find: find its 18th term

34 = a + 6d ………….equation1

64 = a + 12d ………… equation2

Subtract equation1 from equation2 we get

d = 5

Put in equation1 we get

a = 4

So 18th term is

4 + 17 × 5 = 89