The 10th and 18th term of an A.P. are 41 and 73 respectively, find 26th term.
The 10th and 18th term of an A.P. are 41 and 73 respectively, find 26th term.

Answer:

Given,

10th term of an A.P is 41, and 18th terms of an A.P. is 73

a10 = 41

a18 = 73

an = a + (n – 1) d

When n = 10,

a10 = a + (10 – 1)d

= a + 9d

When n = 18,

a18 = a + (18 – 1)d

= a + 17d

 

a10 = 41 and a18 = 73

a + 9d = 41 ………………(i)

And a + 17d = 73…………..(ii)

Subtract equation (i) from (ii),

a + 17d – (a + 9d) = 73 – 41

a + 17d – a – 9d = 32

8d = 32

d = 32/8

d = 4

Put the value of d in equation (i) ,

a + 9(4) = 41

a + 36 = 41

a = 41 – 36

a = 5

an = a + (n – 1)d

a26 = a + (26 – 1)d

= a + 25d

Put the value of a = 5 and d = 4 in a26

a26 = 5 + 25(4)

= 5 + 100

= 105

26th term of the given A.P. is 105.