Question

if 7 times the 7th term of an A.P. is equal to 11 times its 11th term, then 18th term is

Answer 1

Answer:

given

a7*7=a11*11

7(a7)=11(a7+4d)

7a7=11a7+44d

-44d=4a7

-11d=a7

a18=a7+11d

a18=-11d+11d

a18=0

Answer 2

given :-

7 ( a7 ) = 11 ( a11 )

7 ( a + 6d ) = 11 ( a + 10d )

7a + 42d = 11a + 110d

7a - 11a + 42d - 110d = 0

4a - 68d = 0

a - 17d = 0

a = 17d .... ( i )

To find 18th term

a18 = a + ( n - 1 )d

a18 = a + 17d

a18 = 17d + 17d

a18 = 34d