Question

if 7 and 13 term of an Ap be 34 and 64 then its 18 term is??​

Answer 1

Answer:

81

Step-by-step explanation:

Given : A7 = 34

A13 = 64

An = A + (n - 1)d

A7 = A + (7 - 1)d

34 = A + 6d

A = 6d - 34 ——eq 1

An = A + (n - 1)d

A13 = A + (13 - 1)d

64 = A + 12d

A = 12d - 64 ——eq 2

subtract eq 1 from eq 2

A = 12d - 64

- A = 6d - 34

————————

0 = 6d - 30

————————

6d = 30

d = 30/6

d = 5

substitute d in eq 1

A = 6(5) - 34

A = 30 - 34

A = -4

An = A + (n - 1)d

A18 = (-4) + (18 - 1)5

A18 = (-4) + (17)(5)

A18 = -4 + 85

A18 = 81

Therefore , A18 = 81