Question

the 7th and 13th terms of an AP be 34 and 64 then its 18th term is

Answer 1

Answer:8

Step-by-step explanation:

Let 1st term be "a" and common difference be "d" then 7 term and 13 term can be written as a+6d=34......equ.(1) a+12d=64......equ.(2) Solve both equ. We get a=4 & d=5 then So, 18 term be a+17d= 4+17 5 = 899

Answer 2

7th term = 34

=> a + 6d = 34.................eq.1

13th term = 64

=> a + 12d = 64 ................eq2

solving eq. 1 and eq 2 we get

a + 6d = 34

a + 12d = 64

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-6d = -30

d = 5

from eq.1

=> a = 34 - 6d

=> a = 34 - 6x5

=> a = 34 - 30

=> a = 4

therefore

18th term = 4 + 17 x 5

= 4 + 85

= 89