Question

If the 1st term of an AP is 7 and the 7th term is 19. Find its 18th term.

Answer 1

Step-by-step explanation:

using an = a + (n-1)d

where, a is the 1st term, n is no. of terms in A.P. & d is common difference

a1 = 7 = a

a7 = 19 = a + (7-1)d = a+ 6d

subtracting a1 from a7

a + 6d = 19

- a = 7

6d = 12

so, d = 12/6 = 2

a18 = a + (18-1)d

= 7+ 17(2)

= 7 + 34

= 41

Therefore, 18th term is 41.